iDPRT label printer SP410 and SP420 support the most common paper size print 4"x6", and in order to get iDPRT printer used in ShipStation, go to
Settings > Printing > Printing Setup.
Click Document Options to tell ShipStation in which format to create labels and packing slips into the 4"x6" layout.
Keep in mind that all labels in ShipStation are created as 4"x6" labels. Selecting the 8.5"x11" layout will tell ShipStation to rotate the label to fit on the standard size paper.
A mismatch between the selected document options and the paper size set in the printer preferences can have unexpected results, like the document printing too large or too small.
Please refer to the below link for the detailed trouble shooting when you meet the printing problem in ShipStation platform.