If your membership product is not being added to the cart, it can prevent customers from completing their purchase and accessing membership benefits. This issue is usually related to configuration settings and theme compatibility.
Note: The membership will not work until the class and ID have been added to the general settings.form tag and copy the class from the parent tag of product-form

Note: The parent <div> class above the <form> or product-form tag needs to be added.Step 1: Go to the Cart page of the store, right-click on the Checkout button, and click on Inspect.
Step 2: Click on the Checkout button and copy the ID from the button tag.
<div> class of the <form> or product-form is added in the Membership V2 general settings. Missing or incorrect classes can prevent the product from being added to the cart.<form> tag itself.