If your store using other then the Shopify Dawn theme then to make the Membership V2 block work at your front store, you need to configure the checkout button id and product block class into Membership module general setting page.
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A) Follow the steps below to find the product block class:

Step 1: Go to the Product page of the store, right-click on the Add to Cart button and click on Inspect

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Step 2: You'll be able to locate form tag and copy the class from the parent tag of product-form

Step 3: Go to Membership V2 >> Settings >> General settings, paste the class and click on Save class

B) Follow the steps below to find the checkout button ID:

Step 1: Go to the Cart page of the store, right-click on the Checkout button and click on Inspect

Step 2: Copy the ID from the button tag

Step 3: Go to Membership V2 >> Settings >> General settings, paste the copied ID and click on the Save id button