There's a recent change in YouTube's policy. If your YouTube live solution is not working as expected, you just need to re-connect it to solve the problem. Here's how:

Delete your existing YouTube live solution.
Create a new YouTube live solution.
Click the "Select channel" button.
If your YouTube account is not yet connected, click the "Connect..." button.
Follow through the connection steps.
If your YouTube account is already connected, select your target YouTube channel on the popup.
Click the "Next" button.
Click the "Embed on website" button at the upper right.
Copy the embed code.
Remove the old embed code from your website.
Paste the new embed code on your website.

If you need further assistance, please contact support.

Updated on: 10 / 18 / 2021