21266: 'To' and 'From' numbers cannot be the same

You attempted to send an SMS, but the 'To' phone number you supplied is the same as the 'From' number.

You attempted to send an SMS from a Twilio number to itself (i.e. putting the same Twilio number in the 'To' and 'From' parameters).

Ensure you are not attempting to send a message from a Twilio number to itself.