Friends can't see my spawned items on my server. HELP

So me and my friend made a Gmod local server to play together. We both downloaded this vehicle add-on pack and it works for both of us in single player. But when he joins my server i can spawn them but to him they show as errors. And when i go to his server he can spawn them but they just show up as errors to me. So it only works for one of us o each of our servers. Can somebody please show a solution. Thanks!

Are you sure it’s the same vehicle

Positive, we downloaded the same pack. Its just weird that the person that isn’t hosting isn’t able to use them and even see them. When he hosts it i get errors even though i have the add-ons. And when i host he can’t get them.