The google account I use on my phone (and the one I want to use with Join), is a different google account I use in Chrome. (I either use a family google account in Chrome or a work one). When I try to install Join, there is no option to use a different google account than the one Chrome is already signed in to use. I can use different google accounts with both Pushbullet and Mighty Text, as well as Chrome itself. Would be nice to do the same with Join, since I'm pretty sure I need to use the google account my phone uses.