Many people are in the same boat on this issue. I have had a ticket open with 2nd level engineers on this for two weeks providing info/screenshots between a channel that works and a channel that does not work for embedding livestream (same issue as everyone else, Eligible but not Enabled)
All the comments about adsense, 1000 subscribers, etc is NOT the answer. The channel of mine that does not work
1) Is part of Google /Youtube Nonprofits, which gives you a bump without needing all the subscribers.
2) Has a linked and working adsense account
3) Is in good standing
Form the engineers at Google/Youtube
1) Do not need 1000 subscribers or watch time
2) Do not need the adsense account
3) Final message just the other day from them (4/29/2020)
"I received an update from our internal team and basing from their review, your channel is fairly new and you might not have an access to the said features yet. Unfortunately, we don't have a timeline on when this will be enabled, but it should be automatically enabled by our system."
The last is a true statement, this channel is a little over 30 days old. Compared to my other channels that are over a year old and work, looks like it is just a waiting game and not sure how long it will take. UGH :(