Thanks @anders.lund for feedback.
Let me explain how it works. So you are able to customize this template and make it look and function as you desire. Any modification is possible. We strongly recommend to have an intermediate experience with Bubble to easily tweak our template, or at least basic understanding to work with embedded functionality. But if you don’t want to spend time on development yourself, you can always hire a developer to deliver your project!
You are getting support in case there are bugs of template errors on preview, but please note that customization of your app is beyond our support services, unfortunately. But for errors that happen on our side, we’ll certainly fix them so you can use the updated version of this template. 
Sure! We are always using test data in our demo apps with fake data, so you can use test cards but please make sure you enter valid fake card numbers, like this one:
And when you just register a new user, make sure to connect to Stripe as a seller, so this account can receive payments:
So as you already understand, it is required to have 2 accounts and at least one of them should be a connected one to be able to receive payments. And you have to switch to the second one to try to pay the first one for booking.
Hope it helps!