Hello Matt,
Thank you for the provided details. According to the settings, the action should work just fine and for the See Also property the initiator should be able to select only users located in the specified OU. To make sure that all the changes were applied, could you, please, refresh the page of the Web Interface to which the action was added using Ctrl+F5 and execute the action again? Does the issue persist?
Also, please, make sure that you sign in to the Web Interface (not only to the Web Interface Configurator) with the credentials of ADM-Matt Chapman account.