I’m going to be super honest and say that payment APIs are among the more complex to implement, because they have a lot of security!
I’d recommend trying out some easier APIs so that you are familiar with them before beginning this task. (Here is a tutorial of mine that walks you through using an API.)
You say that you can’t use Stripe because you want to set custom prices, but then you acknowledge that the Stripe component lets you set the price - how are you planning on setting the price for each customer? Could we try working out a way to do this with the Stripe component?
Thanks,
Jane