There is no bill from NATO. Member countries are protected regardless of whether they have contributed to the fund. It is an honor system and wealthier nations are more able to afford it. Most nations in Europe have guaranteed healthcare unlike USA so do have budget constraints. And not all countries do well uniformly with their economies.I take it that you don't believe that those who don't pay their bills should be held accountable. Do you also believe a landlord does not have the right to evict a tenant for not paying their rent? Sounds pretty harsh if you do. But that is the way it works. Much easier and cheaper to simply pay the bill rather than get thrown out on the street or have your country invaded. It's up to the country to decide whether or not it is worth it.
I don’t mind there being pressure on countries that can afford to contribute but there’s no reason to threaten them with a bogus consequence. That’s typical Trump, just all talk that’s full of crap.