21265: 'To' number cannot be a Short Code

You attempted to send a SMS, but the 'To' phone number you supplied was a Short Code. Twilio numbers cannot send messages to short codes at this time whether they are Twilio short codes or external short codes.

You attempted to send a message to Short Code.

Ensure you are not attempting to send messages to Short Codes. These sender types cannot receive messages from Twilio numbers.