How I earn a living selling my open-source web-based invoicing application
Please correct me if I'm wrong but this is not how I understand the meaning of "open source software".It sounds rather like customers get source access. Do they have the right to sell the source code or re-release it in any way by following an open source license?
( https://opensource.org/licenses )P.S. I'm not criticizing your business model or anyone elses.