Sometimes when installing new apps or updating the system via the appcenter, you could slip into this generic error: “Failed to fetch updates, This may have been caused by external, manually added software repositories or a corrupted sources file”.
If you click on details,, it will show you the exact repo that gives this error, for example:
Now, here’s how we are going to fix it:
first, open the appcenter and search for “synaptic”, download and open it after entering your password.
Alternatively, you could install it simply by typing “sudo apt install synaptic” into your terminal.
Once opened, go to settings, repositories, and search for the repo cited in the error previously mentioned, click on it, and delete it, click then on “ok”, it will ask you for a reload, accept, and then do a quick restart to make sure all the changes will be applied.
The problem should now be solved and you will be able to update again your system.