WR31 firmware versions previous than 126.96.36.199 only offered access to GPIO settings from the WR31 CLI (Command-Line Interface). GPIO settings were added to the WR31 web interface in Traversion 188.8.131.52 firmware. In order to access GPIO settings from the WR31 web interface, ensure that the WR31 is running firmware version 184.108.40.206 or newer.
TransPort WR31 Analog and Digital Input/Output Interface User Guide
Mar 21, 2019