However it was very clever to give a whole year for free, lock everyone in and then start taking a small fee. I like that strategy. Now with FB it's just a plain data grab.
So I paid for them. Despite them all earning real money in real jobs.
Then Facebook bought WhatsApp, and now none of them are willing to move to Signal, because they like WhatsApp.
That's what WhatsApp did (except that the trial lasted at least one year, and practically often much longer), and it worked wonders for them.
Even better: Offer a full-featured trial, allow incoming messages for free forever, charge the €4 only for outgoing messages after that :)
Maybe free for up to 5 contacts?
I bought the app, I have 3 other people on it, and I've used it to communicate with them sparsely (once a month at most) for over a year.
It's already paid for itself.
I am willing to pay €4. But only if all my friends also pay €4 and decide to start using the app. Otherwise it's worth €0 to me. So unless I can convince them to start (which I usually can't, because they don't trust that their friends will use it), the natural equilibrium is that nobody buys it.
One solution might be a 30 day free trial? I don't know why free trials are so unpopular nowadays. I am much more inclined to buy something when I have had a chance to try it!