I have tested again with "colorful metal" and few other of your FREE skins available on the Play and no one of your skins works now on my Huawei phone. Maybe I was wrong telling that "default dark" was working before. Maybe it was true on one of the previous V3 version of Poweramp (I'm on 816 now), maybe I mixed up with another skin, I cannot be sure now. These days I have tried several skins and only one which is recognized by Poweramp and really working is Material2 skin. Hopes this clarifies and sorry for missleading.
I also have Huawei (Mate 😎 and have the same problem as described in the first post. After install, click on it, nothing happens. They do not appear in Poweramp settings. But this is not happening with all skins: "Poweramp v3 skin colorful metal" and "Yaps - Yet Another Poweramp Skin" are not working, meanwhile "Poweramp v3 skin default dark" is working fine. Any suggestion ?