Choose the same Minecraft version for everyone
Install the same mod loader on every client and server
Download the exact same mods and mod versions
Put the mods into each player’s mods folder
Install any required dependencies or libraries
Use the same configuration files if the modpack requires them
Create or rent a server that supports mods
Upload the server-side mods and config files to the server
Start the server and note the server IP address
Add the server in Minecraft using the IP address
Make sure every player uses the same launcher profile
Verify that all players have the same mod list before joining
Update all clients and the server together when changing versions
Back up worlds and server files before making changes
Use a modpack launcher if you want easier setup
Check that all players have enough RAM allocated
Disable conflicting mods if the game crashes
Join the server and play together