Multiplayer is harder (when hit), than it looks from afar 
I would suggest you get really, really familiar with Networking and Multiplayer in Unreal Engine | Unreal Engine 5.5 Documentation | Epic Developer Community
Other than that - I am assuming only one of your clients attaches the object. What must happen:
- The request for attaching must reach the server through a RPC.
- The server must notify all clients to do the same attachment either through replication or through a multicast event.
Hope it helps and happy reading