MAICPP enrollment: "No billing accounts found" at Choose a legal entity, with an active MCA billing account

I'm trying to enroll my company in the Microsoft AI Cloud Partner Program (ISV, with Commercial Marketplace to follow), and enrollment is stuck at the legal entity step.

Setup

• Company: AGENTICSENSE, a sole proprietorship in Karachi, Pakistan
• Signed in with my work account on our own Entra tenant (agenticsense.co). I'm Global Administrator.
• The tenant has a Microsoft Customer Agreement billing account, AGENTICSENSE, from a Microsoft 365 Business Basic purchase. Its status is Active, my role is Billing account owner, and the sold-to address and registration number are filled in. Its review completed today.

What happens

• At Choose a legal entity, enrollment shows "No billing accounts found".
• Create new billing account completes ("Your account is ready") but returns to the same empty list.
• I retried in a private window after the billing review completed, with the same result.
• I can't open a Partner Center support request, because the form requires a Workspace and I have none until enrollment completes.

Question: How can I get the existing billing account linked to the enrollment, or have a support case opened for it? I can share the tenant ID and billing account ID privately.