Check engine light P0420 – cheap fix or new cat for sure?-Forum-Culture Informatique

That dreaded P0420 code popped up on my 2013 Kia Sportage last week and I’ve been reading forums nonstop trying to avoid a huge bill. The car runs fine, no smell, no loss of power, but the light stays on. I’ve already tried replacing the downstream oxygen sensor and using a can of cat cleaner in the fuel tank but the code came back after about 100 km. I really need to fix failing catalytic converter Dubai without spending a fortune because I can’t pass registration with the light on. I came across Dynostar’s converter page and they mention checking for underlying issues like misfires or vacuum leaks before condemning the cat. Has anyone here had a P0420 that turned out to be a simple exhaust leak or a bad upstream sensor instead of the converter itself? I’m tempted to try one of those spacer adapters on the oxygen sensor but I’ve heard they don’t always work for passing inspection here. What’s the cheapest legitimate way to sort this? Thanks in advance.