Hello @arkiboys . I believe what you need is Synapse Compute Operator to start a pipeline. In your case that appears to not be enough.
I notice that the message refers to the /credentials/useSecret/action . This suggests the pipeline has credentials in it, which require and additional role, Synapse Credential User. (this one is beneath Compute Operator in the image)
Theses RBAC are set withing the Synapse studio, as opposed to the Azure RBAC in the Azure portal.