embedded code

I am experiencing issues with embedding. I am using my YouTube embedded code
<iframe width="560" height="315" src=" https://www.youtube.com/embed/7V127wKncPw" frameborder="0" allowfullscreen></iframe>

I have inserted it to the campaign template. I can see the video image and the click button. I saved it and ran a test email.

The embedded code has disappeared.

It works when adding a video url

please advise