URL       = "https://b24-ar17wx.bitrix24.by/rest/1/ps5...";
    ChatID    = "chat" + "1846";
    MessageID = "33328";

    Result = OPI_Bitrix24.MarkMessageAsReaded(URL, ChatID, MessageID);

    URL       = "b24-ar17wx.bitrix24.by";
    Token     = "14bb8267006e9f06006b12e400000001000...";
    UserID    = 10;
    MessageID = "33330";

    Result = OPI_Bitrix24.MarkMessageAsReaded(URL, UserID, MessageID, Token);