Supported:

Amazon
ebay
shopify
Etsy
Paypal
Fedex（only website）
USPS
stamps.com
shipstation
J&T express
DHL
shipping easy
ORDORO
XPSship
FLASH express
POSHMARK
KERRY express
ninjavan
easyship

For above platforms, before downloading, change label from 8.5x11 inch to 4x6 inch, otherwise, printing may be small and unproper.

Does not support:

endicia
shipworks
shipwire

Use Adobe Acrobat Reader DC with "Snapshot" function:

ups
easypost
shippo

Some platform provide only 8.5x11 inch label, so you need to crop the oringinal pdf file then print. It's suggested to use Adobe Acrobat Reader DC "Snapshot" function.

Also, you may change to other provider and download 4x6 inch label to print.