how can i use my automation vehicles in Beam.MP?

i want to drive my custom cars

that is a bug currently, to use mods in multiplayer, you will need to join a server that has the mods you want to use

@alex-ita but i played with my cars a few days ago in a server, now the mods deactivates alone when i enter to the server

You don’t. You can use the mods the servers offer. If you want to invite your friends into a multiplayer session and play with your cars, you can host a server and add all your Automation cars to it.