a mere trifle; a trivial matter
Used to dismiss something as unimportant or not worth worrying about. Often appears in the pattern 〜は末の問題だ or similar constructions.
そんなことは末の問題だ。
That's a mere trifle.
彼にとって、お金のことは末の問題だった。
For him, money was a trivial matter.
The phrase combines 末 (end, tip, trivial) and 問題 (problem, matter), literally 'a matter of the end' or 'a trivial problem'. The exact origin is uncertain, but it is a fixed expression meaning something of little importance.