Looks OK otherwise

Thank you hippo for that comment...

Your faith in the integrity of it made me go and look again at the endpoint and the settings in Stripe. I found the error which is not what Stripe was making obvious. Digging a bit deeper I found that Stripe was also saying there was 302 redirection. The webhook endpoint in Stripe was subtly wrong causing a redirect which Stripe treats as an error.

Clearly a "senior moment" on my part