Sometimes, a few lines of code are a lot more helpful than an entire documentation...
Simple signup built with TypeScript and ReactJS. Currently restricted to credit card payments.
Simple signup built with TypeScript and Angular 8. Currently restricted to payments via FakeProvider.
A minimalistic signup form built with HTML5, jQuery and ... nothing else. Less than 100 lines.
Simple signup built with HTML5, jQuery. Simple Backend and Admin UI to illustrate REST API usage and webhook handling.