Cannot load the Elasticsearch cluster for your index

In a clean Drupal installation, here is what I see when I open the Search API's main admin page:

However, if you add the server via the Elasticsearch Connector admin form and then open that Search API admin form, then you can add the Elasticsearch server successfully. Further details on how to do this can be found at https://www.lullabot.com/articles/indexing-content-from-drupal-8-to-elas....

Confirming this behaviour.
It works if you add the cluster via admin/config/search/elasticsearch-connector/cluster/add

But not through the Search API Config

I am experiencing this same issue as well.

Same error. #3 works for me.

Is important to check "Make this cluster default connection"

Hello,

If my reply to this issue can help #2986469-3: Error trying to add search API server after having added cluster.

Changed version of issue to 8.x-7.x and uploading a patch to fail gracefully.

#10 don't work for me, the page enter in infinite loop.

In my case the problem come using configuration split, this module settings was moved from general configuration folder to the a split folder. Importing configuration this module become unconfigured, and lock all the site.

#3 worked for me, first you need to add a cluster on admin/config/search/elasticsearch-connector/cluster/add then it will appear on the admin page.

Related: #3563795: Avoid fatal errors if, when adding a new server, certain plugins throw errors