TL;DRCharging for what was measured — events, volume, minutes — instead of a fixed fee.
Usage billing needs a meter, a source of events, and a period. The invoice line for a period is the aggregated quantity times the price, after any included amount, at the tier the quantity lands in.
Usage bills in arrears and is never prorated: a partial period simply measures fewer events. The risk is not the maths but the ingestion — a usage line is only as right as the file or feed behind it.
Where it happens in Sonic
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See it on your contracts
A walkthrough on the agreements and files you actually bill from — not a slide deck.