This is the 10159th most frequent Korean word.
관련자에
"Related person" or "interested party."
In this sentence, '관련자에' refers to the person involved in the situation whom the explanation was given to.
관련자에게 설명했습니다.
I explained to the person involved.
Here, '관련자에' refers to the individual concerned to whom contact was made.
관련자에게 연락을 드렸습니다.
I contacted the concerned party.
In this case, '관련자에' indicates the recipient party associated with the documents' delivery.