If you get paid in some other way such as cash or check you can manually record that payment on the invoice.

To do this; open the invoice > click on the 3 dots menu > click Record Payment.

Click, the + Add button to add a payment.

Add the payment amount, date paid, and payment method. You can click the check box if you want it to send them a receipt.

Click the check mark on the far right to save the recorded payment. This is also where you would go if you wanted to edit a payment made or delete it.

Your invoice will now say paid or partially paid depending on the payment recorded.