I have set up Jira Service management and set the channel access to 'OPEN' and allowed portal-only accounts to be created for new customers that email from a listed domain. This works fine and with an email address from a listed domain I get a new account and can login to the portal. However, when I try to create any request I get the following:

Submitting requests through email works as expected and the user (same portal-only account) can access the support request. What I am overlooking here?