My username generator won't put the names in a textbox or give out any errors can anyone help?

I have tried doing things such as looking at tutorials but I am trying to use this roblox api to check if a username is taken or not taken it is just to generate usernames and I believe it will help me learn lua. This generator does not give out any errors but it doesn't put anything in the output so please help. Since I can not properly format this into the web thing I will post it on a hastebin link https://hastebin.com/raw/ogoliheqoq.php and I have the gui which looks like this and so it won't do anything and I am confused can anyone please help?