That WhatsApp number doesn't belong to the business account you picked in Meta's window.
Before saving, Avox checks that the number is part of the WhatsApp Business Account you authorised in Meta's window. It wasn't, so nothing was saved.
Connect again.
In Meta's window, pick the business account that owns this number.
Still stuck? Send AVX-3114 to hello@theavoxai.com along with what you were doing when it happened.