WhatsApp became massive before being bought by Facebook and you had to purchase it for $0.99 (or $2,99 it's been almost a decade so I can't remember the exact price). So no, as long as the network effect is there, costing money is not a no-go.
Except it wasn't really enforced. They kinda made you think you HAD to pay, but extends it to another year even if you didn't pay. So it was actually free.
