Definition
This idiom is used to convey that the person who provides the money for a particular activity or project has the right to control how it is managed and executed.
Since the company is their investment, they get to make the decisions; after all, he who pays the piper calls the tune.
Although we are experienced, we have to follow the client's ideas because they are the ones paying; he who pays the piper calls the tune.
When the government funds this project, they expect to control the final outcome, which is consistent with the principle that he who pays the piper calls the tune.