WR31 firmware versions previous than 18.104.22.168 only offered access to GPIO settings from the WR31 CLI (Command-Line Interface). GPIO settings were added to the WR31 web interface in Traversion 22.214.171.124 firmware. In order to access GPIO settings from the WR31 web interface, ensure that the WR31 is running firmware version 126.96.36.199 or newer.
TransPort WR31 Analog and Digital Input/Output Interface User Guide
Mar 21, 2019