Invoicing settings must be configured at first, otherwise the module will not work correctly.

In order to do this, go to Settings > Billing and Invoicing

Once you access this section, you will see the following options:

Lets look into them one by one

• This setting allows administrators any status change - including changing void and invoiced invoices
• Note: to delete a void invoice the users (with permissions) must first change it back to 'open'