Correct once you have set up a logical volume then you should be able to create reserved space for the snapshot. Below you should see the function for the number of snapshots that will be available to use. Make sure that you have 4GB for swap and 1GB for system.
Now it works. I have overlooked a message under "Snapshot definition". It said something like "Function not available"(??), but then I was able to choose the number of snapshots.