WhatsApp error 0: AuthException

Code 0 is the Graph API's most basic authentication failure: the token you attached to the request could not be resolved to a valid app user at all. Unlike 190, which tells you a once-good token has expired, code 0 is returned when the platform cannot make sense of the credential in the first place. It is raised before your request reaches any WhatsApp-specific logic, so nothing about your message payload, template, or phone number is being evaluated yet.

Meta lists three situations: the token has expired, it has been invalidated (password change, revoked app, or Meta itself), or the app user has changed a setting that blocks all apps from accessing their data. It carries type OAuthException and HTTP 401, so check the raw body rather than a wrapper's generic "unauthorized".

What is not wrong: your endpoint path, the phone number ID, the recipient, or the message body. Fixing those will not clear a code 0.

Never ship with a user-scoped or temporary dashboard token. Generate a permanent System User token, store it in a secrets manager, and load it at startup so it can never be an empty string. Add a startup health check that calls the token debug endpoint and fails fast if the credential is invalid, which turns an overnight outage into a deploy-time error. If the token is valid but expired you will see 190 instead; the authorization-family triage order is summarized in the WhatsApp error-code guide.