So logstash is able to connect to elasticsearch but when it tries to setup ilm it sends a request to elasticsearch to determine whether the rollover index exists. That is getting an error. The elasticsearch logs may give a better error message to explain why it is rejecting the request.
One possibility would be a 403 (possibly your user has the wrong role ).
Check the elasticsearch logs and enable log.level debug in logstash in case you have a problem with certificates or keys.