TL;DRWhether a line bills at the start of the period it covers or after it ends.
Fixed subscription fees usually bill in advance: the invoice dated 1 March covers March. Usage bills in arrears because the quantity is not known until the period is over. Seats can go either way.
The choice sits on each product line and drives the invoice date, the period shown on the line, and how revenue recognition treats the amount.
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.