In the 'OnBeforeRequest' service of the BoxConnector v2 (I'm using it for JWT access), if user impersonation is set with a user ID, the Authorization Bearer token is not added to the request header and only the As-User is. A List Append on the Request.Header adding the Authorization header is needed before appending the As-User header. Otherwise the calls fail and there is no specific information as to why from the server.