Threats and blackmail
Sometimes leaders pay up out of fear. Sometimes they declare war.
In a call you can demand money with a threat. A leader who fears you may pay, but will resent it. A proud one may refuse and go to war over the insult.
If you have found out a leader's secret, you can blackmail them: pay up, or the world finds out. Paying costs your relations, and refusing may mean war.
Threats work best when you look strong.