Smart Bridge Question

I've searched Lutron's site to find out what the little button is for on the back of the Smart Bridge and can't find a word on it. The bad thing is, I have one PD-6WCL connected and remember not having any issue doing it, but I don't remember exactly how I did it. I'm trying to add three more and things are not so smooth. Lights flash on the new dimmers but the APP just sits there. Does that button play a role in connecting switches?

I'm guessing that one or two of these new dimmers are beyond the range of the Bridge which is a huge shortcoming for the unit.

Thanks for any advice.

The button is used to connect the app to the bridge. It acts as a physical security device so people can't drive by and log into your system.

What is the distance from the bridge to the dimmers? You can add a plug-in dimmer and use it as a repeater/extender.