No branch on Epic. Our ASE maps run the pre-Aquatica build, which Steam players reach through the preaquatica branch (see the guide ASE: cannot join after a game update). Epic has no branches: patch 360.35 says Epic players can roll back only "using third party non official solutions", and the ARK Wiki says "For Epic players there is no official workaround yet".
Crossplay. A Steam-hosted ASE server is visible to Epic players only when it runs with the crossplay settings (-crossplay and PublicIPForEpic). Our ASE maps keep crossplay on so that Epic players can join. Epic players cannot join a modded ASE server, but our ASE maps run no mods, so that is no obstacle here.
The 19-digit id. An Epic crossplay account on ASE carries a 19-digit id that our server plugin cannot address. Anything sent to one character in game — the link code, an admin's private message — cannot reach it, which is why the Link page shows "The game did not accept the message for that character".
Renaming is not moving. An ASE character's owner identity lives inside its profile file, not only in the file name. A renamed file keeps presenting as the Epic player, and the next download at an Obelisk can bring the Epic copy back.
preaquatica branch. Do not rename or move character files yourself: moving an Epic survivor to Steam is an admin job.The admins can move an Epic survivor to a Steam account with a tool made for this. It backs up everything it touches, refuses unless the survivor is exactly the same afterwards — same name, level and experience — and keeps the character's link to its tribe, buildings and creatures. The Epic copy is then retired so it cannot pull the survivor back; a leftover Epic-side copy may still appear afterwards and is retired the same way. After such a move, the Steam account links normally and the in-game code arrives. Crossplay stays on so that Epic players can keep playing, and no server setting removes the Epic id limitation.
Tell an admin the map, the time (the clock in your profile menu shows the server's time), your character's name, what you carried or had uploaded, and the exact message on the screen. For a transfer: both maps and both times. Report the same day — the backups reach back only about two days. Contact admin is in your profile menu; the Guides page has a question box.