I just bought GTAV on steam and I've heard about this bonus. Now I have this xbox 360 account, but the email is a non-valid one and I don't know the password. Can I still get the bonus this way? I also can't send a support ticket because the email is not verificated (not even possible).
You can yes, Just make a new XB account and then go to the new social club account you made for your Steam account and link the new XB account and then sign into that new account on XB and play the prolouge and the next time you log into PC you should get the message letting you know about the RPContent
There used to be a mod that unlocked them for you but it no longer works so above is your only option.