I installed GasStop but it's not working. The gas won't flow through it.Updated a month ago

The most common reason reason is that it has not been primed. After installing GasStop you must pump the valve/propane level indicator to get the gas flowing through it. Give it 5-6 full pumps to start the flow.

Another common reason is simply that the tank is out of propane. 

You may notice that in colder temperatures (approaching 0°C/32°F), GasStop may shut-off more readily when used with higher demand appliances like propane generators, and/or on longer length pipework. For optimum performance during colder temperatures orientate your GasStop so that the gauge is facing the sky.