Has something changed with the Update Account endpoint? It looks like PATCH is no longer accepted as a method.
What does your URL look like? What about your headers and your body?
I’ve tried beta and v3 and get the same response for both.
You need to specify the ID of the account you want to PATCH in the URL. For example:
PATCH https://tenant.api.identitynow.com/v3/accounts/1fe86fc50b0a4171a735ebec0f3af6a6
Try that and let me know if it resolves your issue.