I just bought 1000 coins and upgraded the battle pass to premium. After a “processing” screen I still get the message to upgrade to premium. So it seems, that the upgrade didn’t work but my 1000 coins are gone.
Update:
I restarted the game (bad idea - had 20k ahead of me) but that didn’t work - still had no premium bp. But after that I played two games and now it looks like I own the premium battle pass. I don’t get the “buy premium” any longer. I only have the “buy tiers” button left.