Thanks, @Danny Zollner .
What I'd like to do is get the app featured in the Azure Marketplace, but to do that, it requires a work account (to sign into the Microsoft Partner Network).
Unfortunately the only user in this 'tenant' is the MS Personal one, which has no permissions.
This 'tenant' was created by Microsoft automatically solely because I had an application registered here: https://apps.dev.microsoft.com/
At some point, this was moved to the Azure Portal so I believe some sort of skeleton tenant was created simply to manage this app registration.
It seems to be an "Azure Free" tenant that has no primary domain, but at the same time, no users either.
Ideally I would move the app registration , but since it can't be transitioned, I will try upgrading the tenant with a full license to see if I can then exercise more control over it.