URL       = "https://b24-ar17wx.bitrix24.by/rest/1/ztbe...";
    ChatID    = "chat" + "454";
    MessageID = "8738";

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

    URL       = "b24-ar17wx.bitrix24.by";
    Token     = "c03fa966006e9f06006b12e400000001000...";
    UserID    = 10;
    MessageID = "8740";

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