Due to recent changes in Google’s service, the CoreBOX YouTube app now requires an API key due to recent updates to YouTube’s API access requirements. The good news is that it costs nothing to get API access. All you need is a personal or business Google account and a few minutes to configure your API key and access credentials.
This article provides a step-by-step guide: https://www.firesticktricks.com/create-youtube-api-key.html