V3nD3774, sorry for my irony, i didn't want to offend you.
I just wanted encurage you to read, before getting hands on things... and i guess you didn't visit the link i provided you.

What i was trying to explain you is that 127.0.0.1 is nothing more than your PC. If you have no
Apache server running on your system listening on port 80, or you have no resource on your server named
/SQLInjection/injection.php, you'll never be able to open it. Evidently ZEROF created a vulnerable app by his own hands or downloaded it, and put it in his server, ready to be exploited.
The URL will never be a valid link to you, until you do the same and put in your server a page with the same path and name. That's not an internet resource, but a local one, so it ha no sense asking others if it's a valid link or not...

Sorry for having joked in the first reply.
Have fun!