Request and response
A request is a method (a verb such as GET), a path, some headers (labelled lines of extra information) and maybe a body (the content). A response is a status code (a number saying how it went), some headers and maybe a body. Every feature on the web is built from those two shapes.
Saying "it's broken" gives an agent nothing to hold. Splitting the bug in two does: if the request was wrong, the problem is in the frontend, and if the response was wrong, it's in the backend. That cuts the search in half before anyone reads a line of code.
Say it to your agent
“Before you change anything, log the exact request the page sends and the exact response it gets back, and paste both. Then tell me whether the bug is in the request or in the response, and why.”