When configuring authentication for a JIRA Cloud server, specify your JIRA username, not the email. The username can be found in the user profile.
Converting Strings into Links to Issues
When enabling issue tracker integration in addition to general settings, you need to specify which strings should be recognized as references to issues in your tracker.
For JIRA, you need to provide a space-separated list of Project keys. Since TeamCity 2017.1, you can also load all project keys automatically: check the corresponding box and test the connection to your JIRA server. If the connection is successful, the Project keys field will be automatically populated. Newly created projects in JIRA will be detected by TeamCity and the project keys list will be automatically synchronized.
For example, if a project key is WEB, an issue key like WEB-101 mentioned in a VCS comment will be resolved to a link to the corresponding issue.