A message marked as Undelivered is usually due to a carrier violation. This can occur in a few different ways:
1. Sending SMS from an international number
2. Using the same number to send SMS across multiple positions
To check for this, go to your Company settings and select SMS. To add a number simply select "If you see the regional number and position do not match up, you can change the SMS number like so:
Go into Company Settings > Location Groups > Select Location Group > Select Edit from Actions drop-down> Select the correct number under SMS:
If you have any further questions regarding this, please feel free to send us an email at firstname.lastname@example.org.