Can't figure out the payment system API?

Question

Payment systems

Hello. There is a QubiPay payment system (documentation) - https://docs.qubipay.io/first-steps.html . To work with the API, I chose NodeJS, because. before that I worked with JS, but I don’t understand what and how to do at all. I'm not strong in NodeJS at all, so I don't even know where to start here. I connected the express and QubiPay modules, but the test mode does not start. Krch, please help. At least advice on where to start to connect this payment system