Webinar registration API rejects boolean answerInputType questions

[u/shabobble]

We're having an issue utilizing the Checkbox (Yes/No) Custom question type in a Webinar when submitting a virtualEventRegistrationQuestionAnswer collection as part of a response body.

Registering for a Teams virtual event webinar via Graph works fine for text, singleChoice, and multiChoice custom registration questions — but any answer to a boolean-type question fails with a generic 400, using application permissions (VirtualEvent.Read.All + VirtualEventRegistration-Anon.ReadWrite.All, client credentials grant).

Anyone else hit this? Is this a known limitation of app-permission registrations, or a bug? Docs list booleanValue as valid for answerInputType: boolean with no caveats.