How does Google Play determine location? How do I trick it to think I'm in US? VPN and location spoofer don't work

I just want to buy in-game content from Play Store and I can't redeem the code (with the "need more info" error). It's a US code, my phone has US settings, I cleared all Play data, made an account set in the US, and I use VPN and FakeGps which work on Google Maps, but YouTube and Play still know I'm not in the US right now, and I can't find any more info on what else it uses to tell where I am.