Unexpected token < in JSON at position 4, Notebook server

[VaL]

Hi 

I got NBS running on linux. Federated it with portal.

When trying to open NBS from the tab I am getting 

Unexpected token < in JSON at position 4

error.

This is in the initial setup of NBS, before running the  Administration: Prepare portal items for notebooks.

Any ideas?

[Barış_SerkanAKIN1]

i have a same issue.

installed Arcgis NoteBook Server 10.8 on Windows Server 2019 using Install ArcGIS Notebook Server—ArcGIS Notebook Server | Documentation for ArcGIS Enterprise 

Fedareted to portal over ArcGIS Web Adaptor, NoteBook server validated.

But i can't pass this error