Activate URL Signing on jwplayer.com
Go to your JW Player Dasboard and, on the top right corner, click the image next to your name.
Select Properties from the menu, chose the one you're using and then click to Settings.
Activate the Secure Video URLs and/ or the Secure Player Embeds options.
Activate URL Signing from the plugin options page
Go to the plugin options page and click on the Security tab.
Activate the same options that you've already enabled on jwplayer.com.