After creating an extra charge, you can now choose to generate an invoice for the tenant.
The invoice will be a simple report which prints for just that extra charge. You can choose to either just generate an invoice report which you could print or save, or you can also choose to save the resulting invoice as an attachment against the tenant automatically. This way it will remain on record, and the tenant can view it online via their login.
To create these invoices, edit an extra charge and press the Generate Invoice button.