WISDM Product Enquiry Pro (PEP) is compatible with the caching system if the caching system can whitelist the cookie. If the caching system on your site or hosting server can whitelist the PEP cookie quoteup_wp_session then PEP plugin can work smoothly along with the caching system.
The PEP custom cookie quoteup_wp_session is added to the browser only when the user adds a product to PEP enquiry cart. When the user adds a product to the enquiry cart, the site must load the uncached version of the pages so the Enquiry Cart Icon (usually shown on the top-right corner if the setting is not changed) can show the correct number of products added to the enquiry cart. This will also show the currently added products on the Enquiry Cart page.
WP Engine has its own caching infrastructure and because of which you need to ask WP Engine to whitelist PEP custom cookie quoteup_wp_session. When WP Engine whitelists a cookie, it does not return the cached version of the page if the browser has that cookie.
Not all hostings have their own caching infrastructure, therefore you might use a plugin like W3 Total Cache plugin on your website. Therefore if you are using a caching plugin, then you will have to whitelist PEP custom cookie in your caching plugin’s settings. And after that, the caching plugin will return the uncached version of the pages when the browser has PEP custom cookie.
You can find the setting Rejected cookies to whitelist the cookies in W3 Total Cache plugin under Performance menu > Page Cache sub menu > Rejected Cookies setting.
Here is the screenshot for the same:
