Issue
When attempting to add a phone number to your account as a verified caller ID via SMS you received the error: "The verification has been blocked as this is a restricted country for verifying a caller ID by SMS".
Product
Phone Numbers
Cause
You have attempted to validate a phone number via SMS in a country where SMS validation is no allowed.
Resolution
Validate the phone number via call. See How to Add and Remove a Verified Phone Number or Caller ID with Twilio.