Surprise bill from out of network provider in PA

I went to an in-network urgent care facility in PA back in February for a Covid test. The employees gladly accepted my insurance and copay, but neither they nor the nurse who took the swab ever informed me they use an out-of-network lab (also in PA) to process the sample.

The result was a $400 “surprise bill” I received from said lab. My insurance, Highmark BCBS, which I bought through Pennie (the PA marketplace) confirmed they received 2 claims – one from the UC facility that they paid, and one from the lab that was denied for being out-of-network.

What steps do I take next? I’ve heard the No Surprises Act doesn’t apply to UC settings, but I found PA has a “No Surprises Bill Review Request Form” that includes UC. Do I get the Department of Insurance involved? Appeal the denial with Highmark? Make a big deal to the UC facility about their deceptive practices? Not sure where to start. I’ve already informed the lab that I won’t be paying anything at the moment until I have a better plan of action. I’m not super worried about collections due to the amount, and that I have experience working in collections negotiations and feel I can handle them if it comes to that.