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As per REST connector documentation, authenticationType supported are Anonymous, Basic, AadServicePrincipal, and ManagedServiceIdentity. User-based OAuth isn't supported. Click here to know more about same. But linked service configuration details shows OAuth authentication as well.
As a worked we can consider using Web activity to make API call and get Bearer token and then take token from web activity output json and pass it to main API call to do our desired work. Kindly check below link where similar work-around discussion happened. https://learn.microsoft.com/en-us/answers/questions/52665/how-can-we-authenticate-rest-api-endpoint-via-api.html
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