I think something about the timing of it feels off to me as well. I'm no stranger to payment screens; I grew up playing shareware floppies. I think the difference is that, let's take a game like Monster Bash for example: you can play up until you beat the first boss, and it feels pretty epic, and then there is a splash screen after the epic boss fight which is essentially a "You think that was awesome? Want more? Mail us at XYZ for Episodes 2, 3 and 4 to discover the rest of the journey."

I totally mailed them and had to have more of that.

For this I'm not sure because I don't suggest changing the game drastically, however it feels like there should be some epic fun thingfirst, usually after an hour or so, and then right after that is when you ask the player if they want more. In order for them to pay they would probably need to feel like they already got a very good amount for free and that they now feel generous. This is a cute game but I'm not getting that feeling so I struggle with this.

For the creator: please don't take this as anything negative about the game! It's fun and I like it. But monetization is hard and I'm just offering my previous experiences where I've personally seen it work successfully.