CORS error while adding ServiceNow ITSM connector

I have installed ECK with kibana 8.5.3. I have used logstash to forward the logs to ELK stack. I am able to see the logs in kibana. Now, I am trying to integrate elastic to ServiceNow ITSM for creating incidents for the alerts. When I try to create the ServiceNow ITSM connector, I am getting CORS error.
Note: I have created the CORS rule and created the user as per 8.5 documentation. Also, When I create ServiceNow ITOM and try to test, the severity dropdown is empty. Any help to resolve this issue is much appriciated.