To add product details to your shipping label please follow the following steps
Step 1: Go to Settings
Step 2: Click on General Settings
Step 3: In the Label Setting section check the box in front of Hide Products to hide the details and uncheck the box to unhide the details and click on Save
After saving you will get a message in the top right corner stating "Setting Saved Successfully"
This means you have successfully added the product details to the shipping label.