Getting an error variantRequiresSellingPlan while doing order edit?

My app edits order to add more items. There is an order giving me an error of variantRequiresSellingPlan, the message is “This variant requires a selling plan to be specified.”. What does it mean? The order edit process was stopped due to this error.

My app doesn’t handle subscriptions. Why is a selling plan required? I could only find

https://shopify.dev/apps/subscriptions/selling-plans#configure-a-product-to-be-sold-only-as-a-subscription

which says you set a product to be sold only as a subscription, does this mean it can’t be added in a regular order.

Hi, did you get it managed out?