I have my first stockist on consignment and they have insisted i use an authorised EAN-13 barcode, not the shopify barcode. The cost of a EAN-13 barcode is very expensive so i wanted to explore why they would insist on this.
Have other people encountered problems when using the shopify barcodes when stocking in other stores? What is the difference between the shopify barcode and EAN-13 barcode?
Take the advice you're given and go with EAN-13. Technically speaking there's differences in the number placement but generally speaking UPC is a North American standard and EAN-13 is European.