Someone tell me that after setup the popup/footer bar, they don't see anything happen on their websites. It's because they've not configure the “Time Settings” of this plugin (in “Other settings” panel).
Why they faced with that problem? Because, Wpsubscribers plugin, by default, will show your pop-up/footer-bar only 1 times in a week / per visitor, so they don't have chance to see it again. If you are going to setup a new popup and do testing on it, it's recommend that you set your popup/footer-bar shows many times like this: