In order to get iDPRT to print the labels in Shippo platform, please print your label in a 4x6 in format, which is compatible with iDPRT thermal label printers, navigate to the Labels tab by clicking "Settings" then "Labels." Find the "Default label format" drop-down menu and choose "4x6 in PDF," then save your changes at the bottom of the page.

Please refer to the below link for the detail:

https://support.goshippo.com/hc/en-us/articles/360003876372-Printer-and-Label-Size-Information