Cigna accidentally injury insurance: denied claim after ER visit & hospital stay

I had an out-of-the-blue syncope some time within the last year and had an ambulance trip, ER visit & hospital stay for a week because of this. I have cigna’s complimentary accidental injury insurance policy (offered through my employer). I’m mostly looking to get the $500 they promise for whichever cost more: ambulance or hospital stay (in my case, hospital stay obviously).

I called Cigna prior to submitting the first claim to ask what type of info they needed, and they said mostly just the UB-04 form from the hospital. I obtained that and submitted it, as well as a proof of payment of what I had paid out of pocket vs what my “main line” health insurance paid. Unfortunately they denied it, with message: “No evidence of Covered Accident: no sudden, unforeseeable, external event”.

Fainting for the first time in my life isn’t exactly something foreseeable 😅 So I’m guessing the issue is lack of documentation.

The denial letter also mentions “Initial Physicians Office Visit” as the Benefit Type, which I’m not sure what’s supposed to mean.

Does anyone know what type of documentation they are looking for? It seems like the UB-04 form wasn’t sufficient. Should I provide medical records as well, like the ambulance trip letter, ER admission, any tests I did… what more are they looking for? I plan to call them to get more info, but reddit seemed like a relevant place to try, too.