The application settings are stored in 2 locations:
Default settings are stored in the root directory of the install.
Custom settings are stored in a JSON file in %PROGRAMDATA%\FastClose\ReaderWebAppServer\appsettings.customer.json
The appsettings.json file contains the default settings along with descriptions of their purpose. Do not edit this file: it will be replaced during upgrades.
The appsettings.customer.json file is where you can make modifications to configure your settings according to your requirements.
You can view the complete list of configured settings on the diagnostics page (see below).
There should be no need to change anything in the root install folder.
Usually found at C:\ProgramData\FastClose\ReaderWebAppServer\appsettings.customer.json, the program uses the %PROGRAMDATA% variable to locate the folder. Look for a file called appsettings.customer.json .
Edit your settings file in a text editor.
The C:\Program Files\FastClose\ReaderWebAppServer\appsettings.json file contains the default settings along with descriptions of their purpose. Use this file as a reference.
The appsettings.customer.json file is where you make modifications to override the default settings according to your requirements.
Any settings changes will require a service restart.

See Customizing the FastClose Network Listening Port.
There is a diagnostics page located at /diagnostics.
Enable IsDebug in your App Settings file to see more information on the diagnostics page.
Do not keep IsDebug enabled during normal use.