By default, Poshmark produces labels in an 8.5 x 11 size which won't fit correctly 4 x 6 labels.

 

Update your label size setting on Posh Mark to 4 x 6. 


For  APP：

  1. Go to your Account Tab (@username).
  2. Select My Seller Tools.
  3. Select Shipping Label Settings.
  4. Select a page dimension (4*6)

For website:

  1. Select your profile picture at the top-right of the page.
  2. Select Account Settings.
  3. From the left-hand menu, select Shipping Label Settings.
  4. Select a page dimension.(4*6)


If you are using the app, like the shipping printer app or FBA print, you can share your label to FBA print, or you save the label to file and then open hipping printer app to print.


Reference Link: 

https://support.poshmark.com/articlesDescriptionPage?id=ka01I000000aaxtQAA