Error in connecting to your Youtube account (youtubeSignupRequired)

This error indicates that the user has an unlinked Google Account, which means that the user has a Google Account but does not have a YouTube channel. Such users can access many features that are dependent on user authorization, such as rating videos or adding videos to a watch_later playlist. However, as an example, the user would need a YouTube channel to be able to upload a video. A user who has a Gmail account or an Android device is certain to have a Google Account but may not have already linked that Google Account to a YouTube channel.

This error is commonly seen if you try to use the OAuth 2.0 Service Account flow. YouTube does not support Service Accounts, and if you attempt to authenticate using a Service Account, you will get this error.