To add new additional charge after creating Invoice, please follow the below mentioned steps:
Step 1: Select the invoice >> Click on More >> Click on Edit
Step 2: Click on Additional Charges >> Click on Add New Charges
Step 3: Go to Additional Charges >> Click on New Custom Additional Charge
Step 4: Fill in the details >> Save
Step 5: Now, click on Additional Charges >> Click on Add from existing charges
Step 6: Select the charge >> Fill in the details >> Save