An Integration Procedure that calls an external REST service via an HTTP Action fails with...

The intended answer is C, but the wording is sloppy. A true HTTP 401 normally comes from the external service and usually means authentication headers, tokens, or credentials are rejected. However, OmniStudio/Salesforce outbound HTTP calls also require the target endpoint to be allowed through Remote Site Settings or an equivalent named credential setup. If the API key is confirmed correct and the available choices focus on Salesforce configuration, the most probable platform-side cause is that the external URL is not trusted in Remote Site Settings. API Access permission on the user profile does not authorize an external endpoint. Chainable execution does not cause endpoint authorization failure. Missing Set Values would affect input construction, not Salesforce’s permission to call the URL.

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