Error : fix a 404 Error when using a PPA or updating my package lists.

What can I do if a repository/PPA does not have a Release file?

sample of problem :

When updating, I get the following error message:

The repository 'http://ppa.launchpad.net/mc3man/trusty-media/ubuntu xenial Release' does not have a Release file.

or, another repository/PPA problem ScreenShort in the below:

How to fixing this error :

Step : 1

1. Go to in the Settings and click on the About option.
2. After that click on the Software Updates option.

Step : 2

1. Next click on the Other Software option and then uncheck the options that have already been checked in.
2. After that click on the Close button.

Step : 3

1. The Cache Refresh done this job automatically.

Step : 4

1. Again go to your Terminal and write sudo apt update.
2. And yeah ! Finally your error is gone.

Note: Following this method you can able to solve this type of any repository/PPA issues.