Had the same issue, there is a few problems and I have a working branch. The first issue is the public func GLocalPlayer_FetchItems function is missing the first param as a pointer. However once that was fixed, the callback still didn't work. It seemed to have issues with the string and the struct on the c# side... anyway... there is a branch here that does fix it. https://github.com/muZZkat/unityplugins/tree/muzzkat/fix-fetch-items