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did your friends download the same mods as the server and you also needed to download them in minecraft
you need to install the mods in tlauncher also not only in aternos
alr but anyways you have to do all the steps same in there
there's a copy of the mod folder also, the only one missing on the server is optifine
Share your client log
1. open your minecraft installation path
(enter %appdata%/.minecraft in the file explorer )
2. open the logs folder
3. open the "latest" or "latest.log" file with a text editor
4. copy and paste the content of the file to https://mclo.gs/
5. send the link here
The client log doesn't contain connection attempts to the server
we fixed it by adding the mods 5 by 5, but thank u anyways for ur time 
Why its always said “Failed to synchronize registry data from server, closing connection”
but i already delete config in ( .minecraft ) folder and i check all my downloaded mod all same with server mod. My forge version also same with server forge.
You need the same mods in the exact same versions on your client and server.
