Hi Rahul,
Below are some of the guidelines to troubleshoot this:
1. Check if the match rule scope is correctly set. It should be "EXTERNAL" or "ALL"
2. Test your input data using
scoredmatches API. It should return the expected entity URI if your match rule is correct.
3. If scoredmatches API returns nothing, then use verifyMatches API to further troubleshoot your match rule.
4. If none of the above helps, execute rebuild match table on your tenant, you can even run this on few sample entities if you want.
Hope this helps. Please let me know if you were able to find the solution.