I know how beneficial it is to your business to download the payment receipts. However, this option is unavailable in QuickBooks Online (QBO). You can manually enter the payment receipt into your account. Just follow the steps in the Create and send sales receipts in QuickBooks Online article.
You may also look for a third-party application and connect it to QuickBooks. This way, you'll be able to successfully import your payment receipts to QBO. Please note that only the admin users can connect and manage apps in your account. Here's how:
Go to the Apps menu.
Search for the app you're interested in.
Select the app, then click Get the app now.
Review the Authorisation page and select Connect.
Follow the on-screen instructions to complete the process.