You can keep track of your payments within the 'Payment Requests' section of a proposal. From here, you can add new payment requests and keep track of when they have been paid. Often times, dealers will set a payment request to be due upon proposal acceptance. That way, when a customer accepts and signs a proposal, they are automatically sent the payment request while you have their attention.

Take a look at the "Finn Human" request. You can see that the request has been paid by the customer. Whenever a customer pays one of your requests, you will see that reflected here and you will also receive an email letting you know.