diff --git a/.env.demo b/.env.demo
index 4299371d..6920b998 100644
--- a/.env.demo
+++ b/.env.demo
@@ -3,6 +3,7 @@ WORKDIR=/workdir
 DATABASE_URL=sqlite:///./app/database.db
 REDIS_URL=redis://redis:6379/0
 EXTERNAL_HOSTNAME=docuelevate.example.com
+# PUBLIC_BASE_URL=https://docuelevate.example.com  # Full URL with scheme; required when X-Forwarded-Proto is not forwarded by your proxy
 GOTENBERG_URL=http://gotenberg:3000
 ALLOW_FILE_DELETE=true  # Allow deletion of file records
 COMPLIANCE_ENABLED=true  # Enable compliance templates dashboard (GDPR, HIPAA, SOC 2)
diff --git a/app/api/dropbox.py b/app/api/dropbox.py
index 2707e1c0..73cddec4 100644
--- a/app/api/dropbox.py
+++ b/app/api/dropbox.py
@@ -5,6 +5,7 @@ Dropbox API endpoints
 import logging
 import os
 from typing import Annotated, Optional
+from urllib.parse import quote
 
 import httpx
 from fastapi import APIRouter, Depends, Form, HTTPException, Request, status
@@ -23,6 +24,18 @@ logger = logging.getLogger(__name__)
 router = APIRouter()
 
 
+def _build_dropbox_redirect_uri(request: Request) -> str:
+    """Build the Dropbox OAuth callback redirect URI.
+
+    Uses ``PUBLIC_BASE_URL`` when configured (recommended for deployments behind
+    a reverse proxy that doesn't forward ``X-Forwarded-Proto``).  Falls back to
+    deriving the URI from the incoming request's scheme and host headers.
+    """
+    if settings.public_base_url:
+        return settings.public_base_url.rstrip("/") + "/dropbox-callback"
+    return f"{request.url.scheme}://{request.url.netloc}/dropbox-callback"
+
+
 @router.get("/dropbox/global-authorize-url")
 @require_login
 async def dropbox_global_authorize_url(request: Request):
@@ -43,13 +56,13 @@ async def dropbox_global_authorize_url(request: Request):
             status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
             detail="Global Dropbox credentials are not configured",
         )
-    redirect_uri = str(request.base_url).rstrip("/") + "/dropbox-callback"
+    redirect_uri = _build_dropbox_redirect_uri(request)
     authorize_url = (
         "https://www.dropbox.com/oauth2/authorize"
         f"?client_id={settings.dropbox_app_key}"
         "&response_type=code"
         "&token_access_type=offline"
-        f"&redirect_uri={redirect_uri}"
+        f"&redirect_uri={quote(redirect_uri, safe='')}"
     )
     return {"authorize_url": authorize_url}
 
diff --git a/app/config.py b/app/config.py
index 64701642..70ba5c36 100644
--- a/app/config.py
+++ b/app/config.py
@@ -193,6 +193,16 @@ class Settings(BaseSettings):
     google_docai_processor_id: Optional[str] = None
     google_docai_location: str = "us"  # Processor location, e.g. "us" or "eu"
     external_hostname: str = "localhost"  # Default to localhost
+    public_base_url: Optional[str] = Field(
+        default=None,
+        description=(
+            "The full public base URL of the application, including scheme "
+            "(e.g., 'https://docuelevate.example.com'). "
+            "When set, this overrides the auto-detected URL for OAuth redirect URIs. "
+            "This is required when the application is behind a reverse proxy that does "
+            "not forward X-Forwarded-Proto headers correctly."
+        ),
+    )
 
     # ---------------------------------------------------------------------------
     # Document Translation Settings
diff --git a/app/utils/settings_service.py b/app/utils/settings_service.py
index 58be76d9..644a62eb 100644
--- a/app/utils/settings_service.py
+++ b/app/utils/settings_service.py
@@ -99,6 +99,18 @@ SETTING_METADATA = {
         "required": True,  # Required for OAuth redirects and external URLs
         "restart_required": True,
     },
+    "public_base_url": {
+        "category": "Core",
+        "description": (
+            "Full public base URL including scheme (e.g., https://docuelevate.example.com). "
+            "When set, overrides auto-detected URLs for OAuth redirect URIs. "
+            "Required when behind a reverse proxy that does not forward X-Forwarded-Proto."
+        ),
+        "type": "string",
+        "sensitive": False,
+        "required": False,
+        "restart_required": True,
+    },
     "debug": {
         "category": "Core",
         "description": "Enable debug mode for verbose logging",
diff --git a/app/views/dropbox.py b/app/views/dropbox.py
index db3c3b30..5723650a 100644
--- a/app/views/dropbox.py
+++ b/app/views/dropbox.py
@@ -14,6 +14,19 @@ from app.views.base import APIRouter, Depends, get_db, require_login, settings,
 router = APIRouter()
 
 
+def _get_dropbox_callback_url(request: Request) -> str:
+    """Return the Dropbox OAuth callback URL.
+
+    Uses ``PUBLIC_BASE_URL`` when configured so that the redirect URI displayed
+    to the user (and registered in the Dropbox developer console) matches the
+    one used in the OAuth authorization request.  Falls back to deriving the URL
+    from the incoming request when ``PUBLIC_BASE_URL`` is not set.
+    """
+    if settings.public_base_url:
+        return settings.public_base_url.rstrip("/") + "/dropbox-callback"
+    return f"{request.url.scheme}://{request.url.netloc}/dropbox-callback"
+
+
 @router.get("/dropbox-setup")
 @require_login
 async def dropbox_setup_page(
@@ -30,6 +43,8 @@ async def dropbox_setup_page(
     path from the integration's existing config is pre-populated; global
     admin credentials are never exposed in this mode.
     """
+    callback_url = _get_dropbox_callback_url(request)
+
     if integration_id is not None:
         owner_id = get_current_owner_id(request)
         integration = (
@@ -67,6 +82,7 @@ async def dropbox_setup_page(
                     "app_secret_value": "",
                     "refresh_token_value": "",
                     "global_creds_available": global_creds_available,
+                    "callback_url": callback_url,
                 },
             )
 
@@ -86,6 +102,7 @@ async def dropbox_setup_page(
             "integration_id": integration_id,
             "integration_name": None,
             "integration_type": None,
+            "callback_url": callback_url,
         },
     )
 
@@ -116,5 +133,6 @@ async def dropbox_callback(request: Request, code: str = None, error: str = None
             "app_key_value": "",  # The callback will prioritize sessionStorage values
             "app_secret_value": "",  # The callback will prioritize sessionStorage values
             "folder_path": "",  # The callback will prioritize sessionStorage values
+            "callback_url": _get_dropbox_callback_url(request),
         },
     )
diff --git a/docs/ConfigurationGuide.md b/docs/ConfigurationGuide.md
index fefa9fce..a84ce393 100644
--- a/docs/ConfigurationGuide.md
+++ b/docs/ConfigurationGuide.md
@@ -19,6 +19,7 @@ Configuration is primarily done through environment variables specified in a `.e
 | `WORKDIR`              | Working directory for the application.                  | `/workdir`                     |
 | `GOTENBERG_URL`        | Gotenberg PDF processing URL.                           | `http://gotenberg:3000`        |
 | `EXTERNAL_HOSTNAME`    | The external hostname for the application.             | `docuelevate.example.com`      |
+| `PUBLIC_BASE_URL`      | Full public base URL including scheme (e.g., `https://docuelevate.example.com`). When set, overrides auto-detected URLs used for OAuth redirect URIs. **Required when your reverse proxy does not forward `X-Forwarded-Proto` headers.** | *(not set)* |
 | `ALLOW_FILE_DELETE`    | Enable file deletion in the web interface (`true`/`false`). | `true`                      |
 | `COMPLIANCE_ENABLED`   | Enable the compliance templates dashboard (GDPR, HIPAA, SOC 2). | `true`                      |
 | `FACTORY_RESET_ON_STARTUP` | Wipe all user data on every startup (demo/testing). | `false` |
diff --git a/docs/DropboxSetup.md b/docs/DropboxSetup.md
index 8923a595..b0e44852 100644
--- a/docs/DropboxSetup.md
+++ b/docs/DropboxSetup.md
@@ -128,7 +128,31 @@ If you encounter issues with Dropbox integration:
 1. **Authentication Errors**: Make sure your App Key and App Secret are correct
 2. **Token Expired**: Click "Refresh Token" button on the setup page to obtain a new token
 3. **Folder Permissions**: Ensure your app has the correct permissions enabled for file operations
-4. **Invalid Redirect URI**: Verify that the redirect URI in your app settings matches the one used in the authentication flow
+4. **Invalid Redirect URI**: See section below for the most common cause and fix.
 5. **Rate Limiting**: Dropbox API has rate limits; if exceeded, wait and try again
 
+### Fixing "Invalid redirect_uri" Error
+
+This error appears on the Dropbox authorization page when the redirect URI in the OAuth request does not match any URI registered in your Dropbox app console.
+
+**Most common cause**: The application is deployed behind a reverse proxy (Traefik, Nginx, Caddy) that does **not** forward the `X-Forwarded-Proto: https` header to DocuElevate. Without this header, the server cannot determine that it is being accessed over HTTPS and may construct an `http://` redirect URI, while the registered URI in Dropbox is `https://`.
+
+**Fix**:
+
+Option 1 – Configure your proxy to forward `X-Forwarded-Proto`:
+
+```nginx
+proxy_set_header X-Forwarded-Proto $scheme;
+```
+
+Option 2 – Set `PUBLIC_BASE_URL` in your environment (recommended for most deployments):
+
+```bash
+PUBLIC_BASE_URL=https://docuelevate.example.com
+```
+
+When `PUBLIC_BASE_URL` is set, DocuElevate uses it directly for all OAuth redirect URIs instead of trying to infer the scheme from request headers. This is the most reliable option.
+
+After setting `PUBLIC_BASE_URL`, ensure the Dropbox app console redirect URI matches exactly (e.g., `https://docuelevate.example.com/dropbox-callback`). The setup wizard at `/dropbox-setup` will show you the exact URI to register.
+
 For more general configuration issues, see the [Configuration Troubleshooting Guide](ConfigurationTroubleshooting.md).
diff --git a/frontend/templates/dropbox.html b/frontend/templates/dropbox.html
index 46d4cc6d..6c41bd96 100644
--- a/frontend/templates/dropbox.html
+++ b/frontend/templates/dropbox.html
@@ -104,7 +104,7 @@
       <h3 class="text-xl font-medium mb-4">Step 3: Set OAuth 2 Redirect URI</h3>
       <ol class="list-decimal ml-6 space-y-3">
         <li>In your app's settings page, go to the "OAuth 2" section</li>
-        <li>Add a redirect URI: <code class="bg-gray-100 p-1">{{ request.url.scheme }}://{{ request.url.netloc }}/dropbox-callback</code></li>
+        <li>Add a redirect URI: <code class="bg-gray-100 p-1">{{ callback_url }}</code></li>
         <li>Click "Add" to save the redirect URI</li>
       </ol>
     </div>
@@ -298,6 +298,9 @@ DROPBOX_FOLDER={{ folder_path|default('/Documents/Uploads', true) }}</code></pre
 document.addEventListener('DOMContentLoaded', function() {
   const userMode = {{ 'true' if user_mode else 'false' }};
   const globalCredsAvailable = {{ 'true' if global_creds_available else 'false' }};
+  // Redirect URI for OAuth: prefer server-provided value (respects PUBLIC_BASE_URL),
+  // fall back to window.location.origin for resilience.
+  const dropboxCallbackUrl = {{ callback_url | tojson }} || (window.location.origin + "/dropbox-callback");
 
   // Store integration_id if provided (for per-user OAuth flow)
   const integrationId = "{{ integration_id or '' }}";
@@ -390,7 +393,7 @@ document.addEventListener('DOMContentLoaded', function() {
     startAuthFlowBtn.addEventListener('click', function() {
     const appKey = document.getElementById('app-key').value.trim();
     const appSecret = appSecretInput.value.trim();
-    const redirectUri = window.location.origin + "/dropbox-callback";
+    const redirectUri = dropboxCallbackUrl;
 
     if (!appKey) {
       showModal('error', 'Validation Error', 'Please enter your App Key');
diff --git a/frontend/templates/dropbox_callback.html b/frontend/templates/dropbox_callback.html
index 662bec61..5b2efd3f 100644
--- a/frontend/templates/dropbox_callback.html
+++ b/frontend/templates/dropbox_callback.html
@@ -108,7 +108,8 @@ document.addEventListener('DOMContentLoaded', function() {
     }
   }
 
-  const redirectUri = window.location.origin + "/dropbox-callback";
+  // Use server-provided callback URL (respects PUBLIC_BASE_URL) with fallback to window.location.origin
+  const redirectUri = {{ callback_url | tojson }} || (window.location.origin + "/dropbox-callback");
 
   // Automatically exchange the code for a refresh token
   if (code) {
diff --git a/tests/test_api_dropbox.py b/tests/test_api_dropbox.py
index aacc57bb..8a9c4456 100644
--- a/tests/test_api_dropbox.py
+++ b/tests/test_api_dropbox.py
@@ -416,3 +416,110 @@ class TestSaveDropboxSettings:
         # .env write is best-effort; endpoint should still succeed via DB write
         assert response.status_code == 200
         assert response.json()["status"] == "success"
+
+
+@pytest.mark.unit
+class TestBuildDropboxRedirectUri:
+    """Tests for the _build_dropbox_redirect_uri helper."""
+
+    def test_uses_public_base_url_when_set(self):
+        """When PUBLIC_BASE_URL is configured, redirect URI should use it."""
+        from unittest.mock import MagicMock
+
+        with patch("app.api.dropbox.settings") as mock_settings:
+            mock_settings.public_base_url = "https://myapp.example.com"
+            from app.api.dropbox import _build_dropbox_redirect_uri
+
+            mock_request = MagicMock()
+            result = _build_dropbox_redirect_uri(mock_request)
+
+        assert result == "https://myapp.example.com/dropbox-callback"
+
+    def test_uses_public_base_url_strips_trailing_slash(self):
+        """PUBLIC_BASE_URL with trailing slash should be handled correctly."""
+        from unittest.mock import MagicMock
+
+        with patch("app.api.dropbox.settings") as mock_settings:
+            mock_settings.public_base_url = "https://myapp.example.com/"
+            from app.api.dropbox import _build_dropbox_redirect_uri
+
+            mock_request = MagicMock()
+            result = _build_dropbox_redirect_uri(mock_request)
+
+        assert result == "https://myapp.example.com/dropbox-callback"
+
+    def test_falls_back_to_request_when_public_base_url_not_set(self):
+        """When PUBLIC_BASE_URL is not set, use request scheme and netloc."""
+        from unittest.mock import MagicMock
+
+        with patch("app.api.dropbox.settings") as mock_settings:
+            mock_settings.public_base_url = None
+            from app.api.dropbox import _build_dropbox_redirect_uri
+
+            mock_request = MagicMock()
+            mock_request.url.scheme = "https"
+            mock_request.url.netloc = "other.example.com"
+            result = _build_dropbox_redirect_uri(mock_request)
+
+        assert result == "https://other.example.com/dropbox-callback"
+
+
+@pytest.mark.unit
+class TestGlobalAuthorizeUrl:
+    """Tests for GET /api/dropbox/global-authorize-url endpoint."""
+
+    @patch("app.api.dropbox.settings")
+    def test_returns_authorize_url(self, mock_settings, client):
+        """Test that a valid authorize URL is returned when global creds are configured."""
+        mock_settings.dropbox_allow_global_credentials_for_integrations = True
+        mock_settings.dropbox_app_key = "test-app-key"
+        mock_settings.dropbox_app_secret = "test-app-secret"
+        mock_settings.public_base_url = "https://example.com"
+
+        response = client.get("/api/dropbox/global-authorize-url")
+
+        assert response.status_code == 200
+        data = response.json()
+        assert "authorize_url" in data
+        assert "https://www.dropbox.com/oauth2/authorize" in data["authorize_url"]
+        assert "client_id=test-app-key" in data["authorize_url"]
+        # redirect_uri should be URL-encoded
+        assert "redirect_uri=" in data["authorize_url"]
+        assert "https%3A%2F%2Fexample.com%2Fdropbox-callback" in data["authorize_url"]
+
+    @patch("app.api.dropbox.settings")
+    def test_returns_403_when_global_creds_disabled(self, mock_settings, client):
+        """Test 403 when global credentials for integrations are disabled."""
+        mock_settings.dropbox_allow_global_credentials_for_integrations = False
+        mock_settings.dropbox_app_key = "test-app-key"
+        mock_settings.dropbox_app_secret = "test-app-secret"
+
+        response = client.get("/api/dropbox/global-authorize-url")
+
+        assert response.status_code == 403
+
+    @patch("app.api.dropbox.settings")
+    def test_returns_503_when_creds_not_configured(self, mock_settings, client):
+        """Test 503 when global Dropbox credentials are not configured."""
+        mock_settings.dropbox_allow_global_credentials_for_integrations = True
+        mock_settings.dropbox_app_key = None
+        mock_settings.dropbox_app_secret = None
+
+        response = client.get("/api/dropbox/global-authorize-url")
+
+        assert response.status_code == 503
+
+    @patch("app.api.dropbox.settings")
+    def test_redirect_uri_uses_public_base_url(self, mock_settings, client):
+        """Redirect URI in authorize URL must use PUBLIC_BASE_URL when configured."""
+        mock_settings.dropbox_allow_global_credentials_for_integrations = True
+        mock_settings.dropbox_app_key = "my-key"
+        mock_settings.dropbox_app_secret = "my-secret"
+        mock_settings.public_base_url = "https://prod.example.com"
+
+        response = client.get("/api/dropbox/global-authorize-url")
+
+        assert response.status_code == 200
+        authorize_url = response.json()["authorize_url"]
+        # The redirect_uri must be URL-encoded and contain the public base URL
+        assert "https%3A%2F%2Fprod.example.com%2Fdropbox-callback" in authorize_url
diff --git a/tests/test_views_dropbox.py b/tests/test_views_dropbox.py
index d42b9304..79dad26c 100644
--- a/tests/test_views_dropbox.py
+++ b/tests/test_views_dropbox.py
@@ -144,3 +144,37 @@ class TestDropboxViews:
         assert response.status_code == 200
         assert b"/Documents/Uploads" in response.content
         assert b"Back to Integrations" in response.content
+
+
+@pytest.mark.integration
+class TestDropboxCallbackUrl:
+    """Tests that the callback_url is correctly passed to templates."""
+
+    def test_setup_page_includes_callback_url(self, client):
+        """Setup page should include the callback_url variable in its response."""
+        response = client.get("/dropbox-setup")
+        assert response.status_code == 200
+        # callback_url is embedded in the JS as the dropboxCallbackUrl constant
+        assert b"dropboxCallbackUrl" in response.content
+
+    def test_callback_page_includes_callback_url(self, client):
+        """Callback page should embed the server-side callback URL."""
+        response = client.get("/dropbox-callback?code=testcode")
+        assert response.status_code == 200
+        # callback_url is used as the redirectUri
+        assert b"redirectUri" in response.content
+
+    def test_setup_page_uses_public_base_url_when_set(self, client):
+        """When PUBLIC_BASE_URL is configured, it should appear in the redirect URI hint."""
+        with patch("app.views.dropbox.settings") as mock_settings:
+            mock_settings.public_base_url = "https://configured.example.com"
+            mock_settings.dropbox_app_key = ""
+            mock_settings.dropbox_app_secret = ""
+            mock_settings.dropbox_refresh_token = ""
+            mock_settings.dropbox_folder = ""
+            mock_settings.dropbox_allow_global_credentials_for_integrations = False
+            response = client.get("/dropbox-setup")
+        assert response.status_code == 200
+        # The configured public_base_url hostname must appear in the page (redirect URI display)
+        page_text = response.text
+        assert "configured.example.com/dropbox-callback" in page_text