The NATO commander should send a bill to each nation who is not
paying their fair share. Then see who pays and who doesn’t.
And do it on a yearly basis.
You have raised an issue that is being discussed but unclear.
Are the uncontributed funds in question direct contributions to NATO or individual nations defense budgets calculated as a percent of the specific nations GDP.
I have come to believe that it is the latter. That leaves open the question about sources and amounts for the administrative NATO budget.
Easier to list the nations who are meeting the 2%...there are just 8 out of soon to be 30 nations. All the rest fall short and then some.