How can I sell my modification of the open source engine of the online store?

Question

open source

There is an open source engine called OpenCart
. There is also a 3-year experience with it and many modules have been developed and the core has been partially rewritten.
As a result, there is an improved modification of this engine, not an assembly, but a modification.
How can you sell every copy of your modification without violating any licenses?

Answer 1

Where are the sources?
The GPLv3 license implies that you MUST open source the modified version, if you do not, YOU ARE BREAKING the terms of the license.
And yes, if you do not violate the terms of the license - you can sell a modified copy for any cost.
Read a little on the topic in an understandable language: https://www.gnu.org/licenses/gpl-faq.html#DoesTheG...

Answer 2

Make a service, sell as SaaS.