GPG error: [repository] stable Release: The following signatures were invalid: NODATA 1 NODATA 2 Failed to fetch [repository] Sub-process /bin/bzip2 returned an error code (2) Some index files failed to download, they have been ignored, or old ones used instead.One or more of your installed sources is temporarily or permanently unavailable.
includes many error messages that might not be easy to understand at first, including error messages that come directly from Debian APT.
HTTP/1.0 403 This package is either paid or requires a paid package to function. If you are trying to download a paid package you have not purchased, buy it and then try downloading it again.
If you are trying to download a free add-on to a paid package (for example, a package adding a new option to Color Keyboard), you have to purchase that paid package before you will be able to download this add-on.
You should be able to remove the problematic source by going to Sources and tapping "Edit" at top right.
If you are not sure which one to remove, try removing all of them except the defaults (Big Boss, Cydia/Telesphoreo, Dev Team, Mod Myi, and Zod TTD/Mac Citi).
This is often caused by a download getting interrupted before it finished, sometimes due to network problems and sometimes due to server problems.