AFAIK there are no "NATO payments". There's just an expectation that NATO countries will spend 2% of GDP on defense, and most European countries are far behind that. Germany however has increased its spending in recent years and is getting closer to the mark.

Trump just doesn't understand the geostrategic position of the U.S., where troops stationed in critical countries prevent invasions which would upturn its imperial economic order. Trump thinks the U.S. has stationed troops in SK, Germany, Taiwan for the countries' interests, where they were clearly deployed there to defend its own.