Preview SaaS offer purchase fails at subscription creation

I'm publishing a transactable SaaS offer and testing the purchase flow in

preview. Test purchases used to work, and then stopped working with no change

on our side that would explain it. The purchase now fails at the final step:

"Couldn't process your SaaS subscription"

Earlier attempts also returned "400 Bad Request" from the marketplace SaaS

service during checkout.

Important: this offer previously accepted preview test purchases successfully.

Several went through and created subscriptions. The same flow now fails every

time, for no apparent reason and with no configuration change on our part.

Setup:

- Transactable SaaS offer, tested via the Azure portal preview link at the

Publisher signoff stage.

- Private test plan priced at $0, 1-year term, restricted to my own tenant.

What I have already verified and ruled out:

- The plan resolves and is selectable. The failure page even shows the correct

plan name, so the preview audience and private-plan tenant restriction are

working. The failure is at subscription creation, not plan visibility.

- Buying subscription is Pay-As-You-Go, spending limit off, Enabled.

- Microsoft.SaaS, Microsoft.Marketplace, and Microsoft.MarketplaceOrdering

resource providers are all registered.

- A valid payment method (credit card) is on the billing profile.

- The buyer's market (country) is included in the plan's markets.

- Azure Private Marketplace store exists but is disabled, so it is not blocking.

- I republished the offer to regenerate a fresh preview link. Preview creation

completed successfully.

- It fails identically for the Azure account owner, not just a delegated tester.

So purchases worked before, every setting I can find is still correct, and it

now fails at Microsoft's subscription-creation step.

Questions:

1. Has anyone had preview test purchases work and then suddenly start failing

with "Couldn't process your SaaS subscription," and found the cause?

2. Is this a known platform-side issue? The republish-with-a-small-edit

workaround did not help.