How to fix "unable to find relevant answer"

Hi, I am having trouble with my chatbot as it answers every question with "unable to find relevant answer".

-I tried to use it in the test run but I faced the same problem.
-I already checked all the logic and everything seems okay.
-I checked the knowledge links and they are all working.
-I tried to publish a new version but it didn't help.

I have no idea what the problem could be as my knowledge is not too vast.