I have a development skill "The great courses plus" in my account. 2-3 weeks before it was working fine.
But Now when I say Alexa Open "The Great Courses Plus" it respond
"I couldn't find any enabled video skills. Go to the music, TV and books section of the Alexa app and enable the video provider you want, and then link your account and complete setup"
In my observation I have seen it happens because your skill-invocation-name matches with any app name which is on FireTV as there is a app named "The Great Courses Plus" on FireTV also. Changing the skill-invocation-name from "The great courses plus" to something else" make it work.
Please help me wheather my observation is right or not.