You have now successfully set up the capability on your device. You can browse the repo directly by tapping on its name in your sources list.
Some developers allowed free tweaks to be downloaded as .deb files. However, since repo.packix.com is offline, repo.packix.com download
For archival and educational purposes, here is how the process used to work on a jailbroken iPhone or iPad. You have now successfully set up the capability
A text box will appear asking for the repository URL. Carefully type in: since repo.packix.com is offline