Read the Documentation With a Goal
Work from the brief alone. Write what you would produce — actors, requirements, data, a first slice, your unknowns — before opening anything below it; the exercise stops working if you read the reality first.
You need the store's backend to learn that a payment succeeded. The provider's documentation is several hundred pages (illustrative). You have an afternoon. Say what you will read, in what order, and what you will run before reading more.
Your attempt
Nothing here is checked. It exists so that the reveal below is a comparison rather than a reading.
Following the "accept a payment in 10 minutes" tutorial to the end. It works, it produces a green checkmark, and it never shows the webhook path, because the tutorial chose the synchronous response to keep the video short — so the store ships trusting a signal the provider's own documentation says is not final.
Read this even if you are confident. It is here rather than behind a button because it is the move most people actually make, it produces things that look like a project, and its cost arrives when the first hard requirement has nowhere to go.