If you were using the original version of this plugin (0.1.*) then you will need to update your configuration with your eWeLink username and password (rather than the apiKey and authenticationToken).
homebridge-ewelink-sonoff has been pulled into this plugin homebridge-ewelink, which offers support for many more devices, more features and more responsive device control.
Please refer to the wiki for more information.
If you have any questions or experience any problems then please feel free to create an issue on github.
Thanks
Ben (the new owner of homebridge-ewelink!)