since you probably don't have an account on dragonflux yet and Fluxer Federation is not implemented yet, you need to register here first. (best email us at support@fluxer.fantasydragon.xyz to get approved quickly)
After your registration has been accepted you can follow the invite link (https://fluxer.fantasydragon.xyz/invite/j4f)

Dragonflux is a self-hosted instance of Fluxer, that means we have admin powers and control the server. But until Federation arrives this also means you need a separate account to join, and we need to approve your registration