[Sinch developers docs, HTTP status codes]: blocked_account means the account is blocked, contact the account manager. illegal_number_type means the number type is not legal for the chosen region, send to a different MSISDN. missing_callback_url means a callback was requested with no URL provided, add it via the dashboard or the request body. unknown_group means the referenced group ID is invalid or deleted. Also check the token matches the service plan ID in the call, since a plan/credential mismatch is a common 403-adjacent auth failure.

Context: Sinch SMS API calls fail with 403 Forbidden and a code like blocked_account, illegal_number_type, missing_callback_url, or unknown_group.

## Matched source
Source: Source: https://developers.sinch.com/docs/sms/api-reference/status-codes
Original query: "Sinch SMS API: 403 blocked_account, illegal_number_type, missing_callback_url"
Key terms: account, blocked, callback, illegal, missing, number, sinch, type