When using the pre-order app together with the option app "Hulk Product Options," an issue occurred where regular products could not be added to the cart when clicking the cart button.
This issue was caused by interference between the "RuffRuff Order Limits" (concurrent order limit) feature and the option app's functionality.
We have improved this so the issue no longer occurs when "all restriction levels are set to allow" or when "restrictions are not used on the product page."
If you are experiencing a similar issue, please apply the settings above.