When creating a Bundle as A Product, you are asked to set how you want the bundle to show in the cart and order. This setting looks like this:
Only the Single-BAP can have a selling plan
You can set a selling plan only when you choose to show the bundle as a single product or what we call a Single-BAP.
If you want to learn more about the differences between the options for showing the bundle as a product please check out this article.
How to add a selling plan to the Bundle Product
Find the Product in your Shopify Products:
You can use the "Edit product on Shopify" from the Fast Bundle admin
Or you can search for the product's name in the list of your Shopify products.
Create a selling plan for that product
In order to activate the subscription feature for this product, go to your subscription app (like SUBIFY or RECURPAY) and set a "Selling Plan" for this product.