A message can fail for reasons on the recipient side or the content side:
- Invalid or inactive number — wrong format, or a disconnected line.
- Handset unreachable — switched off or out of coverage for the whole validity period.
- Unregistered Sender ID — some countries block traffic from unregistered sender names.
- Content filtering — operators may block certain words or link shorteners.
Reduce failures
Clean your list to valid international numbers, register your Sender IDs, avoid spammy content, and use a branded short link from eSMS Links instead of a generic shortener.