Enter payments received from the customer by going to the payments section of OASIS and click on the new button. See screenshot below.
OASIS will ask you to select the customer who is making the payment. Select the correct customer and click "Ok"
Type in the Check number, Amount and date received.
Type in the invoice being paid and the amount and then click the "Set" button. Continue for all invoices being paid.
Add any adjustements as necessary, then click on the "Post Payment" check box. With most tranactions the difference will be zero. If you have any amount of the check left, it can be applied to future transactions. Post the payment even with the amount left. The next time, you have a payment to make for that customer it can be applied to future invoices.
In either case, OASIS will ask if you want to post the transaction.
It will ask a second time, select Post again.
Then click "Save and Close"