Try it without a printer
This is not a picture of a receipt. The server draws it with the same code that puts it on paper, and then it rolls out of the slot the way it would at a counter.
How it is built up
A receipt is a stack of blocks. Switch one off and see what is left. The items and the total stay: without those two it is not a receipt any more.
What just happened
01
Your values went up
The fields you filled in were sent as JSON. No document, no PDF, no printer bytes.
02
The server drew the receipt
The template decided what goes where; roughly seven milliseconds of work.
03
It came back as an image
Here it lands in your browser. With a bridge, the same bytes go over USB to the printer.