In SleekTech all rent invoices are created automatically. If you want to create an extra charge for a tenant you will have to create a non rent invoice.
This is how to create a non rent invoice for a tenant:
To charge the owner a commission set rental fee by doing the following, see highlighted below:
By clicking on Set rental fee, a set fee will automatically come up. You can choose to manually change the fee.

Want to know more? Click on the following link
Create recurring charge for tenant