To print Shippo labels in a 4x6 format compatible with thermal label printers, click "Settings" and then "Label" to navigate to the "Label" tab. Find the "Default Label Format" drop-down menu and select "4x6 in PDF", and save the changes at the bottom of the page.
Note: After changing this setting, the label will be printed in the same format as the thermal label printer. Remember, this only applies to new tags created after the change. Shippo will not convert the format of existing labels. Please note that due to the commercial invoice attached, it is not possible to create an international UPS label in 4x6 format (for other carriers, the commercial invoice is created separately in Shippo).