403 Forbidden

I’ve made an app that uses the Monzo API to move money between pots in response to a transaction. It’s been working perfectly for months, and as of yesterday every transaction results in a 403 error (“Forbidden”). I haven’t changed anything, or even opened my app.

I can still authenticate via OAuth, and using the WhoAmI endpoint successfully reports me as authenticated. However, any attempt to add a tag or fill/empty a pot results in this 403 error. It doesn’t look like my code is at fault since it was fine before and nothing’s changed - has anything changed in the API on Monzo’s end?

Any suggestions welcome - happy to provide more details if they’ll help. Thanks