Copy Data Activity Failed with Unreasonable Cause

The screenshots point to a request-authentication mismatch, not the sink. The activity is receiving a real HTTP 401. Your linked-service description says Ocp-Apim-Subscription-Key and token values are required, but the Copy Activity source shows Additional headers empty. A successful Test connection does not prove the final GET request is authorized; it validates the linked-service endpoint and configured Basic credential.

Send the same authentication data the API expects on the runtime request. If APIM requires a subscription key, add Ocp-Apim-Subscription-Key. If it requires a bearer token, add Authorization: Bearer <token>, or use the API’s exact token header. Keep those values in Key Vault or secure authentication headers rather than plain text.

Then reproduce the exact URL, method, and headers outside ADF. A 401 there confirms the API-side contract. If it fails only in ADF, inspect the activity output for the resolved request URI and confirm the factory managed identity can read the current Key Vault secret. The sink is irrelevant until the source returns a 2xx response.