Credit is spent when a seat runs on Our Keys. It comes from three places, and Plan & Billing shows each of them.
Included credit
For the first three months of a subscription, Pro includes $10 a month and Team includes $20 per member a month, pooled on the team's owner. It is granted for the current billing month and spent before any credit you bought. What is left when the month ends is gone — it is the benefit of a subscription, not a purchase. A yearly plan gets the same three monthly allowances, month by month. After the third month there is no included credit, and usage on Our Keys comes out of credit you top up. A plan granted by hand by support has no billing period and no allowance.
Top-ups
Plan & Billing has top-up buttons for fixed amounts — $10, $25, $50 and $100. The payment provider's fee (about 5% plus $0.50) and the 4.5% the product keeps are taken out of what you receive, so adding $10 credits $8.55, and the pane says what is taken before you buy. Where the price you pay includes sales tax or VAT, the tax is not part of the credit either. Purchased credit does not expire.
Auto-reload
With Pro or Team you can turn on auto-reload: when the balance falls below a line you choose — $2 by default, anywhere from $0.50 to $50 — the app charges your subscription's payment method for a top-up and credits it at once. It runs at most three times a day, and if a charge fails the error is shown on the pane and reloads pause until you look. Auto-reload is what keeps the room to one bill: the subscription, with usage past the allowance added to it rather than paid separately.
Seeing where it went
Settings → Usage & Spend breaks spending down by model, by app and by day. Recent credit in Plan & Billing lists every grant and every charge, with what it was for. On the Mac, Workspace & Account has a ceiling for a whole session and another for a single turn; a run stops when it reaches one.