It looks way to dark and I don't know why. Since the two sided foliage shader model is pretty new I can't seem to find a solution on the internet. I followed some video tutorials and they all did the same as I did. I am no pro at this but I got it working the last time I worked with this engine and I would be grateful for any help in order to get it working again.
You'd need to tweak the opacity value, its a little low. This is something that changed a few versions back.
and something else for some additional performance gains: put the Opacity mask texture into the alpha of your albedo.
You can also try to multiply the opacity mask texture with the green or red channel from albedo, change the values a little and not need a roughness map. if done right you can get the values quite close to the actual roughness map but save yourself one texture lookup, two if you add the opacity mask texture into the alpha channel of your albedo.
Thanks for your answer! Increasing the opacity value did not change anything. But I discovered that if I change the albedo texture brightness it gets a lot better. I think the texture itself was just to dark.