You can use the Horizon Client Custom error screen footer group policy setting to add custom help text to the bottom of all error messages that appear in the Horizon Client user interface. For example, your help text might tell users how to contact the help desk at your company.
You must create a plain text (.txt) file on the local client system to contain the help text. The text file can contain up to 2048 characters, including control characters. Both ANSI and Unicode encoding are supported. You specify the full path to this text file when you configure the Custom error screen footer group policy setting.
For detailed information about using the Custom error screen footer group policy setting, see Using Group Policy Settings to Configure Horizon Windows Client.