I have seen on the MessageBird page that they allow the use of WhatsApp API in their service to send WhatsApp from their numbers.
In my case, being Spanish, Twilio does not allow the use of Spanish numbers for business reasons (they do not make a profit).
The MessageBird team, as I understand it, allows the use of their API after a verified channel has been created. To do this, you have to verify the WhatsApp Business account and obtain a number, after that it lets you open a channel.
The case would be to be able to send messages through that channel to WhatsApp numbers.