TL;DRA sent invoice whose due date has passed without full payment.
Overdue is computed from the due date on the document, which comes from the net terms. Ageing buckets — 1–30, 31–60, 61–90 days — group overdue invoices by how long they have been late.
Only sent invoices can be overdue. A partially paid invoice stays overdue for the balance.
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.