Kia Sedona 2005. One month ago I got P0154 code. Two days ago, I got a code P0420.

Question

Hy. I got a Kia Sedona 2005, 160.000 miles. One month ago, I came up with a P0154 code (O2 sensor). I didn't do anything with it. Two days ago, I got a check engine light with the code P0420 (faulty catalytic converter). What could it be? It's the converter or the O2 sensor is causing the problem? Thanks.