The invoice starts from the settlement-price on the relevant day, multiplies by the contract quantity, and then applies the adjustments in the contract specs. Grain adds or subtracts a delivery-differential for quality and delivery point; Treasury futures multiply by the conversion-factor and add accrued coupon interest.
The number is almost never exactly the futures price times the multiplier, which surprises people the first time. For Treasuries it can differ by several percent.
Example: a Treasury note future settles at 110-16 (110.50) with a delivered bond whose conversion factor is 0.9125 and which has accrued interest of $1,240 per $100,000 face. Invoice = 110.50 x 0.9125 x 1,000 + 1,240 = $102,073.
Related: conversion-factor, settlement-price, delivery-differential, stopping-delivery, cheapest-to-deliver