FSx for windows file server Mount issue

The error may occur if the DNS name of the FSx you are trying to mount is incorrect or if the TCP/IP NetBIOS Helper service is not started on the Windows server side.

The following document contains troubleshooting for FSx.
https://docs.aws.amazon.com/fsx/latest/WindowsGuide/troubleshooting.html

Could you please share how are you trying to mount the file share? Are you using the explorer or command line?