The are two scenarios that can causing the Coming Soon Pro plugin to break.

1. Your front end and your admin are on two different domina or urls.
If this is the case then both your front and admin url will need to be on the same domain to support ajax request. Contact us for work arounds.

2. Another plugin has javascript errors and therefor causing the Coming Soon Plugin to break.
If you believe another plugin is breaking the Coming Soon Plugin, try to disable all plugins except for the Coming Soon Pro. See if that works. If it does then start enabling other plugins to see which one breaks the Coming Soon Pro plugin. Once you’ve identified the plugin contact us with the plugin name and we’ll see if we can provide a work around.