You can record payments against an Invoice easily within OpenCRM.

1. To make a payment, open your Invoice and click the Payment button at the top of the screen

2. This will open a pop-up where you can include a subject, the date, and a brief description of the payment, as well as the amount and payment type.

3. Once you have put in either the Net or the Gross pay, the other two will fill in automatically

From this: 

To this:

4. Click Save on the payment pop-up and your Invoice will refresh. The status will be changed to Part Paid and the paid amount deducted from the Amount Outstanding field. 

5. You can see a full history of the payments made against an Invoice in the Payments subtab.

6. When an Invoice has been fully paid, the status will update to Paid and the Amount Outstanding will reduce to zero. The date of the final payment will populate the Paid Date field.