To download a payment receipt in Data Collection, you need to select the payment for which you want the receipt and click on the eye icon that appears on the right-hand side.
When you click on the icon, the following page will open with the details of the transaction and you can download the payment receipt here.
In some cases, the payment receipt may not be available on this screen, but if the payment has a paid status, you can access the same payment in the Payouts list, using the payee's document to search for the transaction.