I looked at the logs on Stripe for the webhooks and they were all 422 ERR (“No signatures found matching the expected signature for payload”).
I hadn’t entered the discourse subscriptions webhook secret on Discourse!
There are two codes on Stripe’s /test/webhooks/ page. I first tried the one on the top right (beginning we_) but it still got a 422 error. Then I tried the one called “Signing secret” (beginning whsec_, presumably for webhook secret – seems obvious now) and it worked!
Thanks for the help. I’ve moved this to Support.