When printing automatically or directly to your printer from Shiptheory (ie upon barcode scan), the print job Shiptheory sends to your printer uses your default print settings.
On a mac / OSX the default print settings are not obvious to find, you'll need to modify them via the OSX Cups interface.
First, open Terminal, which you can search for by clicking the magnifying glass on the top right of your Mac
In Terminal, copy and paste the following command into Terminal, cupsctl WebInterface=yes ,then press Return on your keyboard:
Now, type the following link into your browser's address bar:
http://localhost:631/printers
On the page that appears, click on the label printer whose default settings are being edited. For this example, we are configuring the HP Envy 7640:
Select the printer you want to change settings for and then select Set Default Options.
Depending on the printer you have will depend on the options you have.
You can change any settings you need Shiptheory to use by default. You may be prompted for a login, this is the user/password you use to login to your Mac normally.
If you're still having trouble, just contact support