Membership plans stay subscription-only after you save them

Membership plans are meant to be subscription-only, but a plan could drift so that its product still allowed a one-time, non-subscription purchase in Shopify, letting a customer buy it without subscribing.

What's fixed: saving a membership plan in the panel now re-asserts that its product requires a selling plan in Shopify, correcting the drift at save time. The membership update path also no longer accepts an outside request to change that setting, so it can't be reintroduced the same way.

This applies the next time you save an affected membership plan; it doesn't change any other plan type.