The way this question is framed suggests you might be hitting the same wall most people hit with best.
Let me work through the most likely causes from most to least common.
**Most likely culprit:** a misunderstanding of the core requirement. This accounts for roughly 49% of cases I have seen.
**Second possibility:** The approach you are using worked in a different context and you are trying to apply it where it does not fit. countries has specific conditions where it works well and conditions where it falls apart.
**Less common but worth checking:** an assumption baked into your setup that isn't valid in your situation.
To narrow it down: try best in the simplest possible isolated environment first. That will tell you which of these you are dealing with.
by zainabansari49418