You do not have to pay for your YouTube phone to have background music on the go. Get acquainted with this little and simple trick.
Since you're listening to music on YouTube on your mobile phone, have you stopped the program and stopped music to make things different? This is classic. And you will not be able to listen to music in the background until YouTube gives the Red Payment to the YT official application.
However, there is a method, even though there is no direct application in the YT application. This is done for Android and iOS:
A tragedy to YouTube for Android
You will need Google Chrome to listen to your YT videos on your Android device. Now visit the YouTube website and click on three points in the top right corner of the window.
When you are in this menu, select "Request desktop version". So, you can see videos as if you were a computer. Play the desired videos and accept when you ask if you want to receive notifications.
Now reduce the app and listen to your video, it's easy!
A trick in IOS
You need to use the browser on iOS, but download Dolphin instead of Chrome. Go to YouTube and pick a video and you can play it in the iPhone Control Center.