Open an option set, or click Create option set to start one, and click the field in the preview.
Open Required and tick Make this field required.
Optionally, write the message shoppers see. Leave it empty and the browser’s message shows in the shopper’s language.
Click Save.
Shoppers can’t add to cart until the field is filled in, and Buy it now is hidden on products with required fields. It’s also checked at checkout, so express checkouts can’t skip it.
Still stuck?
Open the app in your Shopify admin, go to Help and click Chat with us, or email [email protected] with your store’s myshopify.com address.