Make sure to enable the ‘Packing Slip’ option from settings. 

Go to settings > Click on App setting > Click on Module and scroll down to ‘Packing Slip’

Generate Packing Slip;

1. Select the Invoice for which you want to generate a Packing Slip.
2. Click on the three dots at the top right corner. 
3. You will find the ‘Packing Slip’ on top.

- Moon Invoice