I sent them request for invitation in which I introduced myself in few sentences, wrote how old I am and why I like naturism, how I participate in it, and I asked them for invitation, and I also wrote them my instagram name so they can check out my profile and see Im a legitimate person, not a bot or some creep, and the next day I got invitation :)
Ill check out the network and write down experiences here, I still have to see how inviting people works...