Weirdly enough, after restarting PC I have been able to buy the cosmetics. Idk if this was a Steam issue or the game, but there was definitely some issue lol.
I believe I responded to your support ticket, but I’ll drop a reply here too.
I’m glad to hear this resolved after restarting!
Historically, this issue tends to occur after players have recently enabled/disabled the Steam overlay. Waiting for a short period of time, or restarting either the Steam client/PC, like you did, should resolve this.