i can guarantee the trainer works, as 1000 people would be posting it's broken. Therefore, you have some other issue..
Injection Failed. This may be normal in some applications.
However some applications this means the trainer is being blocked."
this means likely the game is being blocked by something.
is your version of the game Windows Store?
After you customized your keys, did you go to the trainer's Settings and saved them with SAVE CUSTOM SETTINGS?
The location of the key file is -> C:\Users\YourWindowsUserName\Cheathappens\Keys\ - Should you find an older file in there please delete it prior to customize your keys and try again.
I used the EXP boost option to level up to the level cap (60) on the steam version and have had no problems online or otherwise. You should be fine
Check windows defender, your firewall, anything that could be blocking it. Best thing to do is have all trainers in a folder that is excluded from anything and everything.
Hope that helps,