21710: Phone Number or Short Code is already in the Messaging Service.ERROR: 21710error-21710 page anchorERROR Error - 21710error---21710 page anchor Phone Number or Short Code is already in the Messaging Service.phone-number-or-short-code-is-already-in-the-messaging-service page anchorYou attempted to add phone number or short code that already exists in the Messaging Service.