There are no credits to buy and no per-action charges. Your plan comes with a usage allowance that fills up and refreshes. Light work uses a little; a heavy compliance check uses a little more. You always see what's left.
A rolling allowance that refreshes through the day, for bursts of focused work.
A larger pool that resets on the 1st of each month. Your plan simply sets how big it is.
Run low? Upgrade or wait for the reset. We never hard-stop you in the middle of a project.