The HTTP request is sent from Roblox to the requested resource, but the requested resource denies it on purpose, due to a client issue. This can be you not sending authentication credentials properly, headers that are missing, an incorrect url path, forming your data incorrectly, pretty much any mistake that you can do. It can also be the requested resource actively blocking the IP/machine that tries to communicate with it. In studio the request is made from your computer/IP but in live servers it’s made by a Roblox server/IP. You could try also testing the url in a live Roblox server to see if it changes behaviour.
Usually the status errors starting with 4xx are the ones you can’t ignore, because they indicate you’re doing a mistake. If the error starts with a 5xx it means that the server did a mistake (which can happen randomly once every few requests).
Something you can do to figure out what’s wrong more easily is check the documentation of the API you’re trying to call for that specific status code.