Here's how:

1. Log in to your OpenCart admin panel.
2. Click the Puzzle Icon.
3. Click Extensions.
4. Select Payments (inthe drop-down menu).
5. Select the + for PayPal Express Checkout (in the Payments Module list) to add this module.
6. Once the module has been added, click the Pencil icon to edit the module settings.
7. Configure the following fields:

• API Username - Enter your API username.
• API Password - Enter your API password.
• API Signature - Enter your API Signature.

8. Click the General tab.
    
9. Configure the following:

• Test (Sandbox) Mode- Set to No.
• Default Currency - Select your preferred Currency.
• Transaction Method - Select Sale or Authorization.
• Status - Set to Enabled.

10. Review additional options.
11. Click Save.
12. Click the Puzzle icon then click Extensions.
13. Select Modules from the drop-down menu.
14. Locate the Express Checkout module and click the Pencil icon.
15. Select Status > Enabled.
16. Click the Monitor icon and select Layouts.
17. Place a checkmark in the Checkout option then click the Pencil.
18. Select Content Top (Recommended) or any other placement option where you would like the Checkout button to be placed.
19. Select PayPal Express Checkout Button and click Save.

Refer to our preferred Platforms and Marketplaces Directory for addional shopping cart specific information.