P0421- Warm up catalyst below threshold (Bank 1)- where is this located? on 2004 Hyundai Elantra

I have a 4 cyc single exhaust 2004 Hyundai-
I have one 02 sensor on top of the exhaust manifold; another one just below the flange of the exhaust manifold where the exhaust pipe connects to the exhaust manifold.

1 answer
Your warm-up catalytic convertor is in your exhaust manifold