When you specify a YouTube video page URL directly as the src for an iframe tag,

Refused to display ‘https://www.youtube.com/watch?v=xxx’ in a frame because it set ‘X-Frame-Options’ to ‘SAMEORIGIN’.

this error occurs.

Incorrect iframe src

Using the embed URL format https://www.youtube.com/embed/xxx listed in YouTube’s [Share] - [Embed code] will prevent the error from occurring.

Correct iframe src

That’s all from the Gemba.