If you are using a third-party fulfilment app, you may have run into an issue where these shipping notifications aren't sending to your subscription customers.
ReCharge sends the order information via our API, we then mark all the appropriate API flags to send out a fulfilment notification. However, some third-party fulfilment apps fulfill the order, then they don't specify these flags on their end. When the order is updated with fulfilment in Shopify those flags disappear. As a result, Shopify doesn't know to send them out. Shopify is aware of this issue and is hoping to one day resolve it. When store owners have run into this in the past, Shopify usually recommends they reach out to the fulfilment app to ensure they are passing the appropriate flags along.
In some cases with the fulfilment apps, this might not be a technical override but rather Shopify handles API-created orders differently than the orders created in their own checkout.
In other words - when orders are created via the API, if the fulfilment call doesn't indicate whether a fulfilment email should be sent or not, the default is false. As a result, apps using the fulfilment API may find the default behaviour is different for orders made via the online store (true) versus the API (false).
In these situations, ReCharge may send the following API calls with the subscription orders:
Once it reaches Shopify and is fulfilled via the third-party service, something seems to break. From what we can understand from other Shopify representatives on previous tickets is that the fulfilment app will rely on the default for the online store (true) rather than including an indication that a fulfilment email should be sent, since Shopify defaults API-created orders to false.
We recommend contacting your fulfilment app's support team and request they add an extra API call to their flow to include the above indicators in order for the fulfilment notification to be sent out for API-created orders.