Can't use official Wii U Gamecube adapter.

[ENunn]

I'm getting an "Operation not supported or unimplemented on this platform" error when I try to use my official Wii U Gamecube adapter in Dolphin. I don't know what's going on. I'm running the latest Dolphin build (dolphin-master-5.0-10881). Any help?

[KHg8m3r]

Did you follow this guide? https://dolphin-emu.org/docs/guides/how-use-official-gc-controller-adapter-wii-u/