Issue:
Failed to send SMS to Candidate ID # with mobile number: . ERROR: Invalid recipient
Solution:
This means that the Candidate with ID (xxx) did not have a mobile number and you have tried to send a SMS message to the Candidate.
So the Centricflow SMS system was not able to send the SMS message.
To resolve this you need to find the right candidate with the ID (xxx) and then update its mobile number.
Then the next time you try to send an SMS message this issue should be resolved.