I found my self the issue. The ftb was not the same exact version as his server that is all.
My friend got a server on Serverminer.com
with Revelation FTB installed
He provided me his server adress. But when I connect on his, I get this message: Failed to connect to the server
io.netty.channel.AbstractChannel$annotatedConnectException: Connection Refused no further information
Here's some clues:
-His server is online with 2 people in it. So no problem on his side.
-My windows firewall is inactive
-My router firewall is disactivated
There is 2 main things happening
When I put [his address] - Can't connect to server
When I put [his address]:[port] - I Can suddenly see his server but my mods does not match with his server
Can you connect to other servers fine? Otherwise your friend should contact his host.
IF server has mods, you have to download them manually