Upvote:2
Frankfurt airport has a transit area like many other airports. If your outbound flight from Frankfurt was outside of Germany then you would not need to enter Germany through passport control. So this would be a visa-free transit.
However, this is not the case for you as you need to board a flight from Frankfurt to Munich. As this flight is inside Schengen area then you need a German/Schengen visa to pass through German border first. Then you can board your flight to Munich.