How to fix the Warning: "fail to access some portal pages" inside Snom Hospitality SIP Phone Administration Tool?

The Snom Hospitality SIP Phone Administration Tool reports the Warning: fail to access some portal pages

in the column Operation History:

To fix this, you may need to install or re-install the Microsoft .NET Framework 3.5 . You can download it from the Microsoft official page: .NET Framework 3.5 Download Microsoft .NET Framework 3.5 from Official Microsoft Download Center

Please note that this .NET Framework 3.5 is not installed per default on Windows 11, but needed by the Administration Tool for full featured functionality.

We recommend to close any running instance of the Snom Hospitality SIP Phone Administration Tool before  the installation of .NET Framework 3.5 . After completing the installation the issue should be fixed.

• Page:
  HD series function key configuration in Yeastar template
• Page:
  How can I access the Hospitality phone web interface? (my browser only shows an empty / blank page)
• Page:
  How can I reset the H-Series phones to factory default?
• Page:
  How to fix the Warning: "fail to access some portal pages" inside Snom Hospitality SIP Phone Administration Tool?
• Page:
  How To install HD phone series in 3CX environment
• Page:
  How to obtain the current IP address info on the Hospitality phones?
• Page:
  How to turn off all or certain LED's of the hospitality phones
• Page:
  Snom Hospitality Analogue Phone Configuration Tool
• Page:
  What is the default WiFi SSID and default WiFi password for the hospitality phones HD350W and HD351W
• Page:
  Where can I download the Snom Hospitality SIP Phone Administration Tool?
• Page:
  Which WiFi / WLAN standards are supported by the Hospitality phones HD350W & HD351W?