13802: Dial: No referUrl specified

In order to send a SIP REFER message to an established <Dial> call, the referUrl attribute must be specified in the TwiML. In this case, a REFER was received on a <Dial> call without a referUrl present.

• Your <Dial> TwiML did not include a referUrl or the attribute was misspelled

• Add a valid referUrl attribute to your <Dial> TwiML
• For more information on sending REFER to Twilio, see Refer to Twilio