Why does my Mulberry product protection app fail to fulfill orders?

[Hleb_Siamionau]

Hi!

I'm working on a bug that we have with several of our partners (App name is Mulberry product protection). We are offering extended protection plans for products to customers. On every order checkout, our service is getting hit by webhook, then we check if there is our protection plan line_item and fulfill it if there is some (we are using Python SDK). It works fine for the majority of our partners (dev shop with only our app works perfectly as well), but for several partners our fulfillment fails in 20 - 60 % of sessions. The fulfillment fails with an error "Line item '{line_item_id}' is already fulfilled". But retailers say to us that those line_items are not fulfilled actually.

I've been searching for a solution for 2 days already and haven't found any piece of info that can be a cause of the problem.

My main assumption is that other 3'rd party apps run into a race condition with us on the fulfillment process.

If partners shop URLs and order ids are needed, please let's talk in one-one chat/email session

Thanks in advance!

[Hleb_Siamionau · Accepted solution]

Here is the cause of the issue https://shopify.dev/changelog/post-purchase-fulfillment-holds