LOL
I would not open a WhatsApp account, even if you tried to bribe me. 😉 --No-no-go.
Well, it depends a bit on the sway you have, e.g. if you manage the IT of a small businness or a larger part of your damily/relatives. Those that don't like it have to use SMS or Mastodon or call me.
It is a hard start I agree.
The solution should
run on iOS/Android, PC/Mac if possible.
install easily or be gifted
have a look-and-feel like WhatsApp
Not use native services...