JIRA Software: Importing a project from one cloud instance to another
How can I import a JIRA Cloud application into another cloud instance?
Full backup and restore is the best possible way to migrate cloud instances. Migrating from one project to another is not currently ideal. Check out this article.
To import JIRA Cloud applications, you need a different backup file structure. You should extract the data directory from the export and zip the contents in different files. Also, check out this article on how to restore a JIRA Cloud application backup into another JIRA Cloud application.