Summary
As you add agents to the rosters, you might see an error message if the associated phone number isn't stored in the correct format in the agent profile.
Clicking on Update would reveal a slider with the incorrectly formatted phone numbers which could be corrected then and there without leaving the module.
Alternatively, if the number of phone numbers to be corrected is too high, you can download a CSV file of the incorrectly formatted phone numbers, update them, and upload the file in the Agents section on the Admin page.