I need to migrate most of the current data from company's on-premise confluence (version 5.6.3 unable to upgrade) to the Confluence Cloud.
It seems I'm not able to use the Cloud Migration Assistant for Confluence.
Except for copy and paste, page by page is there any other easy option?
@Jack Zhou Welcome to the community!
Cloud Migration Assistant is best bet when it comes to migrating data from on-premise Confluence Server instance to Confluence Cloud instance.
Space import functionality which is available on Confluence cloud will also not work in your case as it require Confluence Server version above 6.1
Now looking at all possibilities, I can only suggest two work around (if you can't upgrade your existing Confluence Server instance)