Ok so I figured out that input_rewind_btn = "+5" was wrong and I have to use input_rewind_axis = "+5" instead.

But anyways even if I set rewind_enable = true it isn’t activated, when I check it in the retroarch GUI. And even if I activate it there, the rewind doesn’t work. If I push the button I get a short message that says “rewinding” but actually nothing happens.

P.S.: I forgot to mention that I’m using the Retropie 3.0beta2 Image on an Raspberry Pi 2