21704: The Messaging Service contains no phone numbers

This error occurs when you send a message with a MessagingServiceSid, but the Messaging Service has no available senders in its Sender Pool. To send with a Messaging Service, add at least one phone number, Alphanumeric Sender ID, or short code so Twilio can select a From sender for delivery.

• The Messaging Service was created, but no sender was added to its Sender Pool.
• All senders were removed from the Messaging Service, leaving no phone number, short code, or Alphanumeric Sender ID available for outbound messaging.
• Your application sends with MessagingServiceSid and does not provide a specific From sender, but the Messaging Service has no sender for Twilio to choose.
• You expected an Alphanumeric Sender ID to be used, but it has not been added to the Messaging Service or enabled for your account.

• Add at least one Twilio phone number to the Messaging Service Sender Pool in Console, or add one with the PhoneNumbers subresource.
• If your use case requires a short code, provision one and add it to the Messaging Service so it can be selected for delivery.
• If you send one-way SMS to a supported country, enable Alphanumeric Sender ID for your account and add it to the Messaging Service. Alphanumeric Sender ID is not supported in every country and is not available in the United States or Canada.
• Verify that the Messaging Service shows at least one sender in its Sender Pool before retrying the message. If you want to use a specific sender, include a From value that belongs to that Sender Pool.

• Messaging Services
• Services PhoneNumbers subresource
• Alphanumeric Sender IDs in Messaging Services