Audio files has to be in MP3 format. If you are trying to add audio from youtube, you can’t use video url, you will need to extract audio from it first and upload it as an mp3 file. Hope this helps!
I thought we could upload the audio or add an audio URL, being two different things.
I already downloaded the audio file and uploaded it, but I don’t have the rights for that (it’s a band’s song), that’s why I wanted to insert the video link and remove the audio file.
Ah, I see. Those are actually lesson resources.
On the edit lesson page, click on the Resources tab, there you will find “Video” in the dropdown, choose it and add YouTube video link in the top field.
Then just go back to text and Save a lesson.