I completed up to part 6 and didn’t get this error.
I was also able to get the transcript of https://www.youtube.com/watch?v=znZs418fc_c&list=PL7Q0DQYATmvgONvIWsy34aDkAtcdjsQLE&index=20.
( I skipped generateSummary because I didn’t hove no credit of Open AI, though. 
)
so it may only be getting error in your environment.
Whatever the cause of the error, to resolve the problem early, it would be better your repository public or visible somewhere.