I faced similar issues as github.com/stripe/stripe-firebase-extensions/issues/507 and it looks like there is a permission denied issue when the stripe extension publishes the events.

Somehow this is overcome by just pointing a separate Stripe Webhook to your custom event handler. This function didn't even need the configuration of webhook secret or stripe key and only needed the event handling processing logic somehow. But this needed to enable all traffic and unauthenticated requests.

I just went with setting up my own custom webhook function.