You cannot add phone numbers directly in Zoho Forms' WhatsApp Configuration. Instead, you can only create a channel using a phone number that has already been added and approved in your WhatsApp Manager account.

To resolve this:

1. Log in to Meta WhatsApp Manager.
2. Navigate to WhatsApp Manager > Phone Numbers.
3. Add your phone number and wait for its status to be Approved.
4. Once approved, log in to Zoho Forms.
5. Go to Control Panel > WhatsApp Configuration and try adding a Channel using the approved number.

If you have followed these steps and are still experiencing issues, please contact support@zohoforms.com for further assistance.