apt-offline_1.8.2-1_all.deb "not a debian format archive" error

My network is not working on Linux box. I downloaded apt-offline from https://packages.ubuntu.com/focal/all/apt-offline/download Copied it to ubuntu I've run checksum which seems to be fine.

$ shasum apt-offline_1.8.2-1_all.deb 
9584d3d68492b17c01994f9c9fe2775f979ddcba  apt-offline_1.8.2-1_all.deb

Ran this command

sudo dpkg -i apt-offline_1.8.2-1_all.deb

It gave error not a debian format archive

How to fix this issue or how to get correct apt-offline?

If the shasum is good, I don't know why it's not installing. However, there is a dirty hack you can use to install the files manually. You will need to extract the deb package and then copy the files to your system. Unfortunately, dpkg and apt will not know the package is installed so eventually, you will have to fix this problem or manually install future updates.

First, create a working directory and move the deb file into the directory:

mkdir apt-offline
mv apt-offline_1.8.2-1_all.deb ./apt-offline
cd apt-offline

Then, extract the files using the dpkg-deb command like this:

dpkg-deb -xv apt-offline_1.8.2-1_all.deb

Alternatively, if dpkg-deb is not installed (command not found), you can use ar and tar to extract the files instead:

ar xvf apt-offline_1.8.2-1_all.deb
tar xvf dat*

After you extract the files, use the following command to copy the files into your system:

sudo cp -R ./usr/* /usr/

To verify the installation, run the following command:

which apt-offline

and it should return: /usr/bin/apt-offline

Aside from the fact that you won't get automatic updates, the other problem is that you won't have bash completion.