callerId must be the calling number, called number, or a validated outgoing number. Additionally, if the calling leg is a client leg, the caller ID is required and must be a validated outgoing number. See the Dial Verb API Reference for more information.
Carriers may send invalid Caller IDs on Incoming calls to Twilio. If a specific Caller ID is not explicitly defined on the <Dial> verb, the invalid Caller ID will be passed to the destination. This may cause some destination providers to reject the call, and Twilio will mark it as failed.
To work around this, your application should recognize invalid caller IDs, and substitute them with a valid Caller ID to construct the subsequent <Dial>.