Around morning time between 8:30 to 10:30am on weekdays (we are at Eastern Time zone), we are experiencing a lot of (503) Server Unavailable errors or other (50x) errors when creating Order Fulfillment thru API call. But when I check the order data, Shopify actually received and processed the data that we submitted even with the (503) response. What could possibly be happening during this time that will cause these errors? I saw other (503) errors posted in the community but most of them are paging related and when posting large amount of data. In my case, we are merely posting small data comprising of the shipment Tracking No, item ID and item quantity. Outside of the above mentioned time frame, we never have issue. Let me know if there is anything I can check or share to help someone investigate this at the Shopify side.
Typically the header response will include a request ID. If you include one of these for the 503 failures then I think that Shopify support staff can reference it and take a closer look.
Thanks Greg. I changed my API call to capture the RequestID from the response and will will share it here.