The thing, I wanted a phone number-free option for privacy reasons, which can’t be realized when its tied to payments.

But privacy doesn't depend on a payment per se, but entirely on the type of payment method offered (which we don't know yet, as I already stated in my original comment).

Coming back to e.g. Threema: You can buy a working Threema license key using completely anonymous payment, e.g. bitcoin, or even by cash.

Having the option to pay instead of providing the phone number has the potential to be the much more privacy friendly option, if it is done right...