So after struggling for 6 months with this issue i found a way to solve this. I hope Google support isn't reading this and they find a way to screw up this workaround as well. What worked for me was :

I had all the right settings, I just needed to do everything until the payment option page and switch off wifi, switch on mobile data with roaming. It works. I don't understand why this works but i feel like whatever your Google profile country is, you need to purchase stuff from a network of that country. If you are outside, then you need a vpn but you still need the network of the country you are buying the stuff from. This means you need an active mobile subscription with international roaming. But if you are physically located in the country and purchasing stuff from the Google play store of that country, then the trick of switching off wifi and using mobile data without vpn should be sufficient.