The app shows a Shipping total on the invoice. To fill up its value, follow these steps.

Step 1: Create a Shipping Item
Home > Items > New > enter “Shipping Charge” > select Shipping Item as item type > Save
Step 2: Add the shipping item to your invoice
Open an existing invoice > Add Item > look for & select “Shipping Charge” > enter the Rate > Save.
Then look at the invoice Shipping total. It should show the amount you entered.