why has my tubepress stopped displaying videos?

About 5 years ago I setup a WordPress MultiSite website, on my own hosting, and added Tubepress so that it displayed multiple video’s, which it did OK.

Query 1:
I hadn’t checked the website for awhile, but when I checked the website the other day, now it’s not displaying the video’s but this message in a pink box where each of the video’s should be:

‘YouTube responded with an error: Access Not Configured. YouTube Data API has not been used in project (12_DigitNumberHere) before or it is disabled. Enable it by visiting https://console.developers.google.com/apis/api/youtube.googleapis.com/overview?project=(12_DigitNumberHere) then retry. If you enabled this API recently, wait a few minutes for the action to propagate to our systems and retry.’

I went to the suggest location above, but was unable to make much sense of it.

Query 2:
As it’s been sometime since I set this up, I went to the Tubepress website to re-read the user-guide.
But it now seems that I have to pay for Tubepress, see: https://tubepress.com/pricing/
But it was free when I set it up, so do I have to pay now?
And is this the reason that the video’s are not being displayed?

Many thanks.