Why every API key is created with a budget

Every API key is created with a budget already on. The number written on the key is the emails the account's plan includes per month. On the Free plan that is 1,000 a month. The period is monthly.

A key cannot raise its own budget. Raising it is a person's decision, made in the console. When the key has used the budget, the API refuses the send. The refusal's code is agent_budget_exceeded and its message is "Key budget for the current period is exhausted."

One limit, stated as the product enforces it. Free also stops at 100 a day. On a paid plan the day is described as "No plan daily cap; delivery paced per inbox provider." The key's own budget still applies on every plan, and a key budget cannot be set above the emails the plan includes for the month.

The guide that shows the calls is Budgets and the kill switch. What the refusal means, in one page, is what agent_budget_exceeded means.