You are trying to import the .zip file. The Workflow_Vol_Move___c_mode.dar.zip 12 KB is a .zip file. right click on it and do extract. It will create a file named Workflow_Vol_Move___c_mode.dar which is now ready to be imported in a WFA server.
Now before importing you need to look at a few things.
1. What is your existing WFA version. This dar was created with a very old WFA version 18.104.22.168.2. This dar hence can ONLY be imported on a WFA2.2 and below. If your WFA version is higher, then you need to have an intermediate WFA 2.2 and then import this dar on it. Afterwards export the dar from this WFA to a new updated dar. Now this updated dar can be imported in your existing WFA. But this is a tedious process.
2. If you let us know your WFA version, I can give you the dar file which can be imported directly. So that saves you a lot of effort.
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