From the error, it sounds like an organization or project admin has applied a VPC Service Controls Perimeter to your project that is preventing you from creating a workflow template. Generally, these restrictions apply at the API levels, so it's likely you will not be able to use other Cloud Dataproc API methods as well.
You should contact your project/org admin to understand what restrictions the VPC-SC perimeter enforces and how to gain access. The VPC-SC Troubleshooter may be helpful in determining which policy is being violated by your request.