Active only means the product can be sold in Shopify; it still has to be available to the Google & YouTube channel and meet that channel’s product and shipping rules.
Set the automatic discount’s Purchase type to Subscription or both purchase types as intended; subscription carts won’t qualify for a one-time-only discount.
Advanced features can take up to 24 hours to activate across your channel; pin from the comment’s More menu on the video watch page, after checking that comments are available for the video.