If you added http://cydia.karen.xyz (not secure), try changing it to https://cydia.karen.xyz. Some older package managers (like old Cydia installations) may fail with HTTPS; in that rare case, use http://, but https:// is preferred for security and reliability.
Do not use http://cydia.akemi.ai or https://cydia.akemi.ai.
Use instead: https://cydia.karen.xyz
Note: The old
akemi.aidomain may redirect, but many users report persistent errors unless they manually switch to thekaren.xyzdomain.
The server is generally stable, but you can verify if it's down for everyone:
Result: You have AppSync Unified installed without ever needing the source to refresh.
Sometimes, Karen (the repo maintainer) updates the repository structure. Old links to specific .deb files break, or the Release file changes its syntax. If you haven't updated your jailbreak tools in years, the older Cydia version might not support the new encryption standards.