Custom dialog window on an old game

Job ID: 36357421

Budget: $50 – $120 USD

I want to customize an old 2d MMORPG game with a new dialog window. Specifically, I would like to add dialogue to the game. I do not have a script or any content yet, so I need help creating the script and other content.
What I`m looking for:
Hooking up the game client and creating a custom dialog window that should activate on a specific packet received, more precisely on event invites.
Example: https://prnt.sc/GW1KnkJnYb9b
The dialog should contain 2 buttons and the text it receives from the packet (string.)
On clicking ok it will send a packet and on cancel, it will close the dialog.
I already have the send / receive function.
More information on chat.
The code should be written in C++.
I think the game uses MFC (Microsoft Foundation Class).