Cannot add my number to Voice/SMS channel

Are you using Twilio?

Have you used this number to create a WhatsApp bot? If yes, you will need to delete the WhatsApp bot and remove the connection on the WhatsApp channel. Then add the number again in Voice and SMS channel.

You can use the same number on both Voice and SMS channels but these 2 are incompatible with the WhatsApp channel.

A Twilio number connected with UChat Whatsapp bot cannot be used for anything else.