If you view this error, you dont active apply tax for this product. You must active apply tax for this product. If you dont know how to do, you can read Installation step.
If you view this error, your license is not valid or expired. Check your license.key file or buy a license.
If you view this error, your module folder not include license.key file. You must re-download module files in gleox.com clientarea and copy license.key file to whmcs_dir/modules/addons/g_invoices .
If you view this error, your license can’t verification in license servers or cant read license.key file. You must change license.key’s permission to 766.
If you dont solve problem, please submit a ticket.