Are your payment forms not working correctly for logged out users, or intermittently, with the WP Fastest Cache plugin? Follow the steps below to ensure WP Simple Pay functions as expected with the WP Fastest Cache active.
You do not want your payment form pages to be cached. You can use Exclude Page to exclude those pages from caching.
In the WP Fastest Cache settings, choose the Exclude tab. Click the Add New Rule button which will open the Exclude Page Wizard.
Choose “Is Equal To” in the drop down and then paste in the slug of your payment form page. Click Save. Repeat if there are other pages.
The documentation for WP Fastest Cache lists other methods of excluding pages, and you may want to bookmark it for future reference.