On donation day, we send the payments we've received from the retailers to you. If the amount is less than expected, it may be because some donations are still pending or confirmed but haven't been paid by the retailer yet (not ready for payment). We have more information about this here: Donation Day Payments Explained.
You can keep track of the total amount ready to pay on your transaction summary page. You can find this by selecting Donations on the left-hand menu of the Admin Dashboard.