InvoicePlane is a free software and it will never be a commercial product! We appeal everyone to respect the open source InvoicePlane project and our work and refrain from selling the application as their own product!
What you can do: offer paid professional support or hosting for InvoicePlane.
However InvoicePlane is an open source software released under MIT license. This means that you can use the code but the InvoicePlane name and the logo are copyright of Invoiceplane.com and Kovah.de
This means you have to use another name and logo for the product and include the original InvoicePlane license in the code.
For more information about licensing please visit the InvoicePlane website.