How can I make ServerTravel function work with dedicated server?

I am trying to use ServerTravel(URL, true) to change server and client levels seamlessly.
However, after the server calls ServerTravel(URL, true), the client seems not to connect to the server go into the new level.
I got this error when i do ServerTravel: LogNet: NotifyAcceptingConnection: Server “MapName” refused

My situation is almost similar as this post: How can I change the level for all connected clients in a multiplayer game? - Multiplayer & Networking - Epic Developer Community Forums

Anyone knows how to solve this problem so that I can load levels seamlessly?

Thank you for your help.

You ever solved this? I have the Same Problem. My dedicated Server is on a vserver and Clients can join but if i use travel seamless nothing happends