Quick answer: The 4166, 1899 clue is best approached as a map-coordinate challenge, not as a keypad code. Bring a map reader and a field player before revealing a full solution.
Spoiler-light hint
Unlock the map system first. Locate the area from the number pair, then use an obvious nearby landmark to make sure the field team is searching the intended space.
Team setup
One player stays with the map or records coordinates; one player checks the physical location; both teams confirm each move before changing roles.
If nothing happens
Verify the order of the two numbers; search nearby surfaces as well as the visible object; reset the positions of the map reader and field player before retrying.
Source & update note
Core platform, player-count, crossplay and hosting facts are checked against the official Big Walk FAQ. This page uses spoiler-aware community route notes and should be rechecked after game updates.