how to use DDE.Initiate and with whatsapp desktop

Question

i want to use dde.Initiate to write message in whatsapp desktop but i have this error message ora-106556

    declare
    ConvID PLS_INTEGER;
    whatsapp varchar2(2000) := 'C:\Users\`enter code here`AMMAR\AppData\Local\WhatsApp\WhatsApp.exe';
    begin
    convID:=dde.app_begin(whatsapp,DDE.App_Mode_MAXIMIZED);
    ConvID := DDE.Initiate('???','???');
    end;

but i couldn't please help me!!!!