Changes to Sign a custody contract on behalf of the session's group

added the optional property error/authorization to the response with the 400 status

added the optional property error/authorization to the response with the 409 status

added the optional property error/authorization to the response with the default status

added the non-success response with the status 400

added the non-success response with the status 409

api tag customer-session added

added the optional property error/api_client_id to the response with the default status