I am developing a transactional email API and would like to test it with the test portal, but I can't seem to get it to work. I get the "This hub doesn't have access to some HubSpot features that are required by this integration. Please contact the integrator." errior. My test portal is a Marketing Enterprise portal. I'm assuming it is because transactional emails require an add-on, but I don't see an option for it. Is it possible to test transactional emails in a test portal environment? (I know that I have the correct scopes because we were able to add it to our production portal.)