thanks for your answer. Do I need to change that gamma value?
Follow
this guide for which textures Poliigon require gamma 2.2 (srgb) and gamma 1.0 (linear)
I tried downloading the same texture once with metal workflow and once with specular. With the metal workflow I get a good result. With the specular one not. The material is almost completely black.
Use the metal workflow in my opinion. Corona Physical Material works well with this.
I was told by someone to put the Reflection map in the IOR slot. That why i did it.
Nope, don't do that. That's incredibly bad advice.
If you want to know more about IOR and
reflectance (not
reflection!) You can read more about it in
an article I wrote some time ago (now outdated for Corona but the concept is still relevant for fresnel IOR).
Reflectance (at f0) and
reflection textures are quite different to each other and if you are using the metal workflow, don't bother with IOR, leave it at the default values (unless you have some understanding of how IOR works).