Are you receiving the 1 on from UE4 on your Arduino or are you sending the 1 from your arduino to UE4? If you are doing the latter, I would suggest using an “is equal to” function and a true/ false branch if you need an event to occur if it receives a 1 because I don’t believe you can give input to the “A pressed/ A Released” function in the blueprint.
What are you trying to accomplish by setting the 1 equal to meaning A pressed/ A Released?