Failed to launch the unreal multi user server


I have a problem with multi user server, when I try to launch a server I get this message. (look the bottom right corner)

Can you help me please ?

Thank you

Someone to help me please ?

We Use Squad editor.
When we use UE 4.25.1 with Multi-User plugin we have no problem but when we use Squad editor we have same message.
Moreover when i go to installed pluggin, multi-user server was not installed.

Do you have solution?