How does the connection with the payment service work, in my example?

Question

PHP

I'm digging into EasyPay. When creating an order, I have to send a post-request to the service with order data and store data. That is it is clear, we send the form with the data.
But they write that before submitting the order, I must create a connection between the systems POST {{host}}/api/system/createAppor perform a page refresh. POST {{host}}/api/system/createPage
I can’t figure out how to do this and why this is necessary. I would be grateful for help. Here is a link to the instructions (found only a saved copy) https://webcache.googleusercontent.com/search?q=ca...

Answer 1

the response has a pageid, which is passed in the headers when creating a payment