Currently, I am testing out how to setup subscriptions on a Shopify store with a headless setup. I connect my Nuxt frontend to the store through the Storefront API with GraphQL. I have been looking at several subscription apps (eg. ReCharge and Native Subscriptions), but I am facing problems when sending the line items to the checkout. I use the checkoutLineItemsAdd mutation (https://shopify.dev/api/storefront/reference/checkouts/checkoutlineitemsadd) but cannot send the selling plan along to pick up the subscription (and subscription discounts) in the checkout.
Can you help me clarify whether it is possible at the current state of Storefront API/headless setups for Shopify stores or not.