21212: Invalid From Phone Number (Caller ID)

You attempted to initiate an outbound phone call but the 'From' phone number you supplied was not a valid phone number. Twilio accepts phone numbers in E.164 format (i.e. "+1 format"), and 10-digit US and Canadian numbers with any combination of non-digit separators, or up to 11 alphanumeric characters [a-zA-+00000-9]. The number must not be on the do-not-originate (DNO) list.

Incorrect number entry

Check the From number

https://en.wikipedia.org/wiki/E.164

https://en.wikipedia.org/wiki/North_American_Numbering_Plan