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On this page we give you answers to the most relevant issues and problems. If you don't find an answer to a problem, please contact our support for further information.

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Why do some SMS show as undelivered? What can I do about it? [Q1066]
Undelivered messages typically fall into a few categories:

Invalid number – the recipient number does not exist or is incorrectly formatted. Always use E.164 format.
Phone switched off or out of coverage – the message may be retried automatically until its validity period expires.
Network filtering – some operators filter messages from certain originator types or content patterns, particularly on prepaid numbers.
Regulatory blocking – certain countries restrict specific sender types or require local registration.

Review delivery reports (DLR) via webhook for per-message status codes. Regularly cleaning your contact list of permanently unreachable numbers improves delivery rates and reduces costs.