Hello,
If you take a look at the way ioset rule is configured, it only sets the output pin to high state.
To set output state to low using SMS you would need to configure additional SMS rule.
For this, login to router's WebUI, navigate to Services -> Mobile utilities -> SMS utilities. At the bottom of the page add a new rule by giving it an SMS text, for example ioreset with Action set to Change I/O state. In the rule configuration window enable it, set State option to Low and save the settings.
In order to execute it, send the following SMS to the router:
- <routers_password> ioreset
Best regards,