Hi @mft ,
Can share the exact input you provide to the pub.string:lookUpTable service , for the input lookupTable and other inputs if any? I tried with input lookupTable as Ø O and passed key as Ø, I see the value O in the results.
You can add a screenshot with a sample input if it helps clarify the problem.
Also please mention the version and fix of the Integration Server you are working with.