Okay. I managed to link my RE.net account to my PS4. I don't know if this is going to help anyone else do it, but this is the way I did it.
Go online and log into RE.net. When you log in, there should be a button to press that says PS4, towards the left corner of the screen. Then there should be another button where you press the PS4 option. (Can't remember if it's next to the Revelations 2 option).
Anyway, hopefully you can figure that part out. It'll then ask you to link your PSN ID to your Capcom account. Follow the steps to log into PSN and then you should have your accounts linked. Then go on your Revelations 2 game, press options, test the connection and hopefully it should work.