The most reliable method while the repo is down is manually installing the .deb file. The rootful DEB for AppSync Unified (iOS 5+) can be found via GitHub releases.
If the above steps don't resolve the issue, you can try: cydia.akemi.ai not working
Very old versions of Cydia (iOS 9 or earlier) may not support modern TLS, causing connection failures. The most reliable method while the repo is
The repository cydia.akemi.ai (Karen's Repo) is currently experiencing technical issues and downtime. As of late 2024 and early 2025, the owner, akemin-dayo (Karen) cydia.akemi.ai not working
Let me know if it starts working for you again, or if you have a mirror repo.