Where is stock O2 sensor location?

Hi first post. Did some exhaust work and replaced everything from the cats down to the tailpipe.

My question is where is the location of the downstream o2 sensor supposed to be? Long story short, the muffler shop welded in an o2 flange in between my two new cats (looks kind of janky), and that’s where the downstream o2 sensor sits now. I think they just copied what was there before and used the same location from the previous owner/ shop. When I took it in, I gave them a diagram that showed the o2 sensor after both cats, but they obviously didn’t follow it. I asked about it when they were finished, but they insisted it was good and that was the stock location. I currently don’t have a check engine light. Is it worth going back or should I just run it? Thanks!

2004 Tacoma TRD 3.4l V6

 

Rear sensor will be after/behind the last cat. IIRC, it’s located on the pipe going to the muffler

i would go back and get it redone

 

I'm curious is it generating a code CEL