As a free service to our customers and to prevent them from unnecessary cost, we check all phone numbers used on to see whether they are valid or not. An invalid format can mean:

  1. It does not exist at all or
  2. It was provided in an invalid format 

so sending towards this these numbers would fail anyhow but would result in a charge for both and for our customers.

To check number validity, we recommend this 3rd party tool:

We will only completely prevent sending in case a campaign is configured to go to 100% invalid numbers.


If only a part of all numbers of a campaign are invalid, we allow sending to avoid unnecessary interruptions by forcing our users to clean their list of numbers before being able to send.

We will not attempt to send an SMS to invalid numbers in the campaign, to prevent you from incurring unnecessary costs. Instead you will see such cases with status REJECTED in your Message Log.

If you have any questions, please send an email to