I am trying to use a Twilio phone number for Apple's two factor authentication, but when I set up the phone number on Apple's site the initial verification SMS is never received by the Twilio number. I have confirmed that Apple is able to send the text to a Google Voice number. I have also confirmed with Apple support that the message sent is a standard SMS. Is there something on Twilio's side preventing receiving the message?
This is actually by design. By default, Twilio long code numbers can't receive SMS messages from short code numbers. Look for the section titled "Are you expecting to receive SMS from a short code?" at the following link. https://support.twilio.com/hc/en-us/articles/223133447-Not-Receiving-Incoming-SMS-and-MMS-Messages-on-Twilio-Phone-Number
When I asked this question the functionality wasn't available at all, but now the feature can be requested. There are caveats. https://support.twilio.com/hc/en-us/articles/223181668-Can-Twilio-numbers-receive-SMS-from-a-short-code-