My website now only displays the above error code when I click on a YouTube video linked there.
In SD I use the Video platform and Enter the Video Url It is the embed code provided by YouTube. For example, video URL = https://youtu.be/LNH1JOM4hUE.
When I enter the URL directly into the browser, I am taken to YouTube correctly, but when I use it in SD, the website displays the error message. What have I done wrong? ...

Mich ael When mousing over your youtube video link on your post here a url appears in the lower part of the screen that is the same as the link on your post if you then click on it it goes to the video as you state. I propose that you go to your site and mouse over the link that is giving error and mouse over it and see if the url which appears with that mouse over is correct, if it is correct and you still get the error I do not know what to say but if it is wrong you can then fix it and possibly get rid of the error message and successfully link to your video from your site.

Hi GregB, thanks for your idea. This is queer I have different web sites that showed this problem for youtube videos (and never did before) and now they play fine again. I had checked aginst Vimeo embedded Videos and those played fine. So I thought it is a youtube thing.
Searching in the Internet it said that youtube has changed something in December for the embed code - but now all is playng again. so sorry for the wrong alarm