I’m also experiencing this issue. I double checked with the Jira admin and we have the Jira user and the testrail settings. We also have the Jira TestRail plugin fullly working, we just can’t push issues to Jira at the moment.
I’ve configured test rail to point to Jira, it looks like it is able to pull the projects, however it’s not able to select several of our actual engineering projects. (it is able to push to our help desk tickets)
Plugin “Jira_REST” returned an error: Invalid user or password or insufficient permissions for the integration user (HTTP code 401). Please make sure to use your actual JIRA username for the integration (not your email address, for example).