I've followed this thread, but as it's closed I cannot reply to it.
I'm getting the same error, but cannot locate any of the jQuery code in my theme.
I've started to receive the error after installing and activating Ninja Popups.
If I de-activate Ninja Popups, the 403 error disappears.
Is this an issue with the plugin? or is the Theme affected when the plugin is activated.
I'm using the Avada theme.