The application itself requires no license to use if you’re self-hosting. The $20/year is simply to remove the Invoice Ninja branding from the client-facing areas of the application (client portal, invoices, etc). To remove all branding, you would need to join their reseller program.
Someone referred me to invoice ninja about a year ago. I actually have found it to be great and the service too.
I feel that I am going to be using it for a very long time so I don’t mind paying $20 for the branding removal on the clients side.
I would like to try reselling. But I haven’t recieved a reply to the email I sent through.