Hustle optin plugin not working

Hey looks like a great plugin but I cannot get it to work.

Tested on 2 websites - works fine on one with loads of other plugins (No caching plugin installed) will not work on the other site which HAS got wp supercache installed.

So, I have deactivated wp supercache and reverted to a simple twenty fifteen theme, still not working.
Deactivated all plugins still wouldn't work! Cleared the cache still nothing, I decided to uninstall the hustle plugin and re-install it, to check if it may have been a corrupt install, still won't work.

I have also noticed that when re-installing after deleting the plugin, it still retained all the info? I don't see how this can be as I have no caching activated - is this plugin leaving data on the data base and not cleaning up? Help, I really would like to use it :slight_smile: