How many Twilio numbers or senders can I have in a Messaging Service? – Twilio Support

A Twilio Messaging Service can contain up to 400 Twilio message senders by default, including phone numbers, short codes, Alpha Sender ID, and WhatsApp senders.

If you reach this limit and try to add additional senders to your Messaging Service via API request, you will receive an Error 21714 response.

Requesting to increase sender pool limit for a Messaging Service

If you need more than 400 message senders in a single Messaging Service, please contact Twilio Support about a Messaging Service sender pool limit increase.

If you reach out to request a sender pool limit increase, be sure to include:

Your Twilio Account SID
The Messaging Service SID you are requesting the increase for
How many senders you wish to have in your Messaging Service (your requested limit)
A description of your messaging use case and why you need a higher sender limit