Visited an ENT and need help understanding how this system works (live in CA)

Sorry for the broad title but I’m a (relatively) new immigrant from Australia and our system is completely different.

I have health insurance through my employer – Blue Shield of California Platinum Full PPO 250/10 OffEx

I went to see a specialist (ENT) which I know costs me $10 per visit – which is fine. The doctor apparently performed a nasal endoscopy on me (Code 31231 according to their invoice). At the time I just assumed this was a standard part of the process.

However, I’ve since received an invoice which seems to have treated this as a separate procedure as I’ve now been charged a total of $259.50 for the whole thing. Itemized it looks like:

New Patient Appointment (99204) $235.00

Nasal Endoscopy (31231) $345

Patient Copay -$10

Primary Insurance Payment -$310.50

Total $259.50

I guess I’m just super confused why that nasal endoscopy wasn’t covered in full? When I looked through the ‘Summary of Benefits and Coverage’ document I got from Blue Shield when I was signed up I didn’t really see anything suggesting this wouldn’t be covered.

Also, and just more broadly, I had no idea what was being performed on me, that it was needed, and whether or not it was covered at the time it was being provided. How are you supposed to make a decision on what treatment to receive if you don’t know that information? Do I need to ask at every step of an appointment with a doctor if what they’re about to do is covered by my insurance?