devtrackers.gg
The game was running in the background, and I purchased through steam, while my Ubisoft Connect overlay was disabled. (I suspect this is why it went wrong.)
Alt-tabbed back into the game - and nothing happened.
Restarted the game, now with the Ubisoft Connect overlay active (to get the in-game store to work).
The One-time offer is listed (in game) as not purchased. If I hit "buy" it says "thank you for your purchase", but i still don't recieve any credits when backing out of the store.
If I could, I would have just refunded the purchase through steam to try again - but it's listed as non-refundable.
Help me, Ubi-wan. You're my only hope.