Thank you for the links. Unfortunately, I’m not quite smart from the instructions, because I do not know which parts of the link must be changed or is it enough if I change the link as follows?
https://api.twitch.tv/helix/streams/"+TwitchID+"?client_id=ls2awgx5gfg9m1q6iopdqb1b7d0y6a
I replaced “kraken” with “helix” and “nickname” with “TwitchID” like recommended but it’s still not working. 
Could please someone change the link so that the script works again or have other parts of the script in the source code to be changed? Unfortunately, I can not do it myself. But maybe someone could look at the affected file “stream-status-for-twitch.php” and change it accordingly. That would be a great help to me.