I did some research on it, and I can't seem to figure it out. I know you have to connect the player to the GUI somehow but I could never figure it out. Whoever helps i'll gladly upvote ^-^
it's a bit similar to this but not exactly.
I also checked this wiki page and got no results
Simply make the gui on the client, if Filtering Enabled is set to true.
You could also follow the advice of the answer on the question you linked:
You can put the billboard Gui inside of the players PlayerGui, and set it's Adornee to the part you want it on. Then only that player will be able to see the gui.