But many NATO countries have had a decrease in military spending since 2006 when this agreement was signed and have shown no real intention to get up to this level. Now it's perfectly reasonable to say that this is fine and the 2006 agreement isn't that big of a deal. It's also very reasonable to say that good relations are more important than everyone meeting their goal and a clear commitment to Article 5 is essential. But sergiotapia's comment that countries should pay their fair share is also reasonable and ajross's response that NATO isn't a pool of money misses that point.
With all due respect, that's missing the point. If you believe that NATO is a good thing and successfully deters aggression against its member states, Trump's near-abrogation of America's treaty commitments objectively did far, far more damage to that deterrence than Germany underfunding its army. Ergo, Trump's nonsense about "paying" and your defense thereof seems terribly insincere. Either you don't believe in NATO's mission, or you are confused about how it works.