I believe you only need a unique phone number to create the account, then you can use WhatsApp Web as client. Be very careful with alternative clients, as I've had an account banned in the past for this (and therefore a phone number blacklisted), even without messaging anybody. I think that clients that run WhatsApp Web in a web view (like https://github.com/rafatosta/zapzap) are safe.
I think they started banning unauthorized API users around the time that "WhatsApp For Business" was introduced, because it was competing with that product. Unfortunately WhatsApp For Business is geared toward physical products and services with registered companies, so home automation and agents are left with no options.
I believe you can use a virtual number/VOIP (like Twilio or Google Voice), but I want to be able to eventually use SMS where WhatsApp can't be used, so I do know some services identify "non residential" SMS phone numbers (for example I've seen Google Voice numbers blocked) so I wanted to prevent that from happen. Again, key thing here for me is that my assistant appears to be a human.
I think they started banning unauthorized API users around the time that "WhatsApp For Business" was introduced, because it was competing with that product. Unfortunately WhatsApp For Business is geared toward physical products and services with registered companies, so home automation and agents are left with no options.