When people are working on free software, they would like to be paid for it. Of course
this conflicts with the fact, that the software itself is free of charge itself. One
can charge money for additional services like file hosting, server hosting, community
services, support and so on. But it does not change the fact, that software itself
can be used in principle by anyone.
A classic approach to tackle the problem is to raise money through funding platforms.
One idea was to display advertisement in the terminal during the installation process of the open
source program.
One other solution is to have the core application being FOSS while selling non-FOSS extensions. In such a constellation such extensions can be made FOSS when the functionality of
such extensions becomes common enough that it is not critical for funding anymore.