Error type: “Bad Request”. Error message: “Bad Request” Domain: “usageLimits”. Reason: “keyInvalid”.
Did you added your own Google API key? Look at the help.
Check in YouTube if the id PL9vjL6653edkAprZpdkDRw9w39sgqA7k0 belongs to a playlist. Check the FAQ of the plugin or send error messages to support.