We’ve created a daily polling mechanism to check the billing API response for each and every user.
Moreover, the Shopify billing API will report a user’s plan as valid even though his store is no longer active.
For example, a shop is to be billed on April 15th, but the shop is frozen/cancelled.
The billing API will still report the subscription charge as active and billed on April 15th.
The billing API will only report the billing is inactive on April 15th.