id from its creation response.
Endpoint
id — a UUID — not its wallet_ref. Wallets belonging to another account return 404, and so does a value that isn’t a well-formed UUID, so a 404 handler catches the “I passed a ref by mistake” case too.
There is no lookup-by-wallet_ref endpoint. Since the ref is your own identifier, re-POST it to create wallet instead: that call is create-or-get and returns the existing wallet.

