The instructions on SMS gateway configuration is available [here](/docs/settings/configuration/sms-account).
- Check if the **SMS gateway** works properly.
- Check if `sms.notSent` event is generated on the customer's activity list. If so, check the event parameters to see the source of the issue. It may also be caused by time limits imposed by the SMS provider.
- Check if `sms.capping` event is generated on the customer's activity list. If so, the message wasn't sent due to the limit of SMSes that can be sent to a customer in a defined time frame.
Learn more about [capping configuration](/docs/settings/configuration/campaign-limits).
- Check if the customer meets the requirements to receive the text message (a valid phone number and a valid marketing consent).
- Check if the template is built correctly.
- The number of allowed characters.
- If your message contains special characters, make sure the gateway accepts special characters.
- If [snippets](/docs/assets/snippets) were used in the SMS template, make sure that the item of information you want to display using a snippet (aggregate, expression, first name, and so on).
- Check if this issue concerns only selected recipients or the whole audience - look for `sms.send` or `sms.notSent` on their profiles.
- If some customers didn't receive the message, check if they belong to the audience of the message.
- Check the status of SMS (it can be still in progress).
- Verify if the SMS communication is not deleted.