We recently encountered an issue with the Shopify POS system orders.
On the Shopify POS system, unlike in the browser, a customer email is not required to place an order (in the case where the receipt is printed and handed to the customer, not emailed). When an order is placed without an email, FetchApp cannot deliver it, because we don't know where to send it without a customer email address.
To combat this issue, we are making an adjustment to FetchApp when Shopify orders come through with no emails. We will now send a successful response to Shopify (so as to not interfere with your webhooks) but we will also send you (the merchant) a notification via email that an order was placed without an email.
Moving forward, if you are letting users create POS orders for digital goods via FetchApp, please remember that they will need to either use an existing customer account or create a new one (we require a first name, last name, and email address) during checkout.
Please feel free to write into firstname.lastname@example.org or comment on this thread with questions.