Choosing a license for commercial software

Question

Law in IT

Please tell me in the direction of which license for your paid (!) Program you should look, under the following conditions:
1) The source code is open
2) The source code can be modified
3) You can write plugins and sell them
4) But you need to pay for each installed copy of the program (or take permission) to the author

Answer 1

GNU GPL

Answer 2

The GPL suits you just fine. Distribute the code under the GPL, and the installer under a closed license (and naturally unmodifiable).

Answer 3

It is strange that the GPL is suitable, because this license does not prohibit compiling your executable module from source code and not paying for a license. So in its purest form, the GNU GPL is not suitable. Or you need to use a dual license - proprietary and GPL, as, for example, in Qt. Or another similar move.
Please note that if you choose the GNU GPL, then you will have to make all modifications and edits to the source code available later. Or you will have to change the license to another one. In this sense, the LGPL looks preferable.
Strictly speaking, your requirements should be clarified. Do you want even a program built from source code to have to pay (ask for permission) or does this only apply to your build? In the second case, you can try the GPL, but evaluate your strengths, can you act as RHEL in a RHEL / CentOS bundle? In the first case, it is better not to open the code at all.