html iframe youtube not working code example

Example 1: iframe youtube not working

<iframe width="560" height="315" src="https://www.youtube.com/embed/ZwKhufmMxko" frameborder="0" allowfullscreen></iframe>

Example 2: iframe youtube playlist not working html

<iframe width="560" height="315" src="https://www.youtube.com/embed/videoseries?list=PLQGSXoAiT2W4W8D3397nl4OB_GxfOmJk9" allowfullscreen></iframe>