Error : failure - 400 Bad Request from POST https://users-migration-service.prod.atl-paas.net/api/users/migration/jira when using Jira Cloud Migration assistant

Issue Summary

When performing a migration from JCMA, we observe the error as shown in the screenshot below:

[user, group] migration completed: failure - 400 Bad Request from POST https://users-migration-service.prod.atl-paas.net/api/users/migration/jira

Steps to Reproduce

• The issue appears when jira server has invalid users with the email address domain like @...localhost , @...localdomain , @dummy.local.
• Run the Jira Cloud Migration assistant, to migrate users and project to the Cloud site.
• Run the Migration plan.

Expected Results

Jira cloud migration assistant detects these invalid emails during pre-flight checks.

Actual Results

We observe the error below when migration users and groups:

 [user, group] migration completed: failure - 400 Bad Request from POST https://users-migration-service.prod.atl-paas.net/api/users/migration/jira 

Workaround.

None.
Contact Atlassian support so they can help investigate this through the logs.