Google Identity Toolkit failing to sign-up new user: Error code: Internal error encountered

Question

New users trying to setup logins that aren't @google.com are hitting issues using Google Identity Toolkit. This has been working fine for a long time so not sure what's up. Looks like this:

In the console seeing a 500 error coming back when calling this URL:

https://www.googleapis.com/identitytoolkit/v3/relyingparty/setAccountInfo?key=<key>

POST data:

{"email":"nlckeweo@sharklasers.com","displayName":"test","password":"password"}

API response:

{
  "error": {
    "code": 500,
    "message": "Internal error encountered.",
    "errors": [
      {
        "message": "Internal error encountered.",
        "domain": "global",
        "reason": "backendError"
      }
    ],
    "status": "INTERNAL"
  }
}