If you are using the "WP Super Cache" plugin, you may encounter some issues when visiting the checkout. This is due to aggressive page caching (which is a good thing!), but it can be easily resolved by excluding the checkout page URI from the cache plugin.
You need to exclude checkout pages by following these instructions-
Step 1: Note down the slug of your checkout page from the general settings tab.
Step 2: Open the settings of “WP Super Cache” and click on "Advanced" tab.
Step 3: Scroll down below to the section where we need to add the string for the checkouts pages.
Step 4: To exclude "checkouts" pages enter your noted checkout page slug (from step 1) with special characters as shown in screenshot: "/checkouts/"
Step 5: Click on "Save Strings".
Note: By default, Checkout page's slug is "checkouts". If you had changed the checkout pages slug for any reason get the slug from WooFunnels > Settings > General > Permalinks