YouTube Channel version 3 requires YouTube DATA API Key to work…

Hi!

I did all you say to do, but I got this message on my widget area:
YouTube Channel version 3+ requires YouTube DATA API Key to work. Learn more here.

Also, in my admin panel, I see this message:
Please note, to make YouTube Channel plugin v3+ work, generate YouTube Data API Key and add it to wp-config.php file as we explained here.
If you already did this during 3.0.0-Alpha test period, please rename constant name from GOOGLE_API_KEY to YOUTUBE_DATA_API_KEY.

If you have any issue with new version of plugin, please ask for help on official support forum.
This notice will disappear when you add missing key as mentioned above!

I cleaned all the catches but these messages simply don’t disappear.

Glad if you can help me.
Thanks,

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