Integrating Square and Magento usually requires the purchase of an intermediary system for synchronizing order and product level data. The largest issue we have faced is the case when the SKU of a product is not necessarily the same as the UPC barcode for a product. Variations of data and/or missing barcode data on certain products, can force a Magento store to use a different value for SKU numbers than the actual read-out from a UPC tag.
