Here is a sample Postman sample showing how to add a new page to a PDF using Qoppa PDF REST API.
The width and height are defined in points at 72 DPI so an 8.5 inches x 11 inches page are defined as 612 x 792.
It’s a form data that is being sent with one (key, value) pair for the pageAction.
Here is the json file entered as value to the pageAction key pageAction.json (remove .txt extension after downloading).