Payment or funding models have never been the problem. Those are menus you choose from, not tricky parts you have to come up with from scratch. Thinking of a single product idea I feel has enough chance to succeed to be worth working on, is the entire problem.
After 25 years of never once thinking of one, I doubt that's going to change.
Seriously? Payment and funding are what matter when you are self-bootstrapped, wanting to make an income, and not intending to sell your company (to someone who will likely just destroy it). If instead you want VCs to own you, or intend to not turn a profit, then payment and funding don't matter.
After 25 years of never once thinking of one, I doubt that's going to change.