    URL    = "https://b24-ar17wx.bitrix24.by/rest/1/av5...";
    ChatID = "3390";

    OPI_TypeConversion.GetLine(ChatID);

    ChatString = "chat" + ChatID;
    MessageID  = "67534";

    Result = OPI_Bitrix24.MarkMessageAsUnreaded(URL, ChatString, MessageID);

    URL       = "b24-ar17wx.bitrix24.by";
    Token     = "a5b00469006e9f06006b12e400000001000...";
    UserID    = 10;
    MessageID = "67536";

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