First need to set mySms as default then you can switch back

For people having problems, I solved mine but setting mysms as my default texting app on my phone and sending a few texts that way. They went through, and then I switched my default texting app back to Hangouts and so far the web app and chrome extension/app are still working. I guess it needs mysms as the default at first to establish a connection?

firefoxer26 about mysms - SMS Texting & Sync