13220: Dial: Invalid ringTone value

This warning is returned when a <Dial> verb includes an invalid ringTone attribute value. The ringTone attribute lets you override the ringback tone Twilio plays to the caller while executing <Dial>.

• The <Dial> verb included a ringTone value that does not match one of Twilio's accepted ringtone overrides.
• A custom ringtone override was supplied with a value outside the documented ringTone values for <Dial>.

• Update the <Dial> verb so ringTone is one of the accepted values for ringTone.
• If you do not need to override ringback, omit ringTone. When it is not specified, Twilio will play ringback or pass ringback from the carrier if one is provided.

• TwiML for Programmable Voice