If you are trying to replace the straight path with the spiral, then you must make the spiral a continuous path instead of multiple paths. Try after selecting all the paths of the spiral and use Object>Path>Join.
This worked! Thanks, Larry
You can only replace with a single path. You have several here. Use the spiral tool perhaps to create your continuous path.
I wanted to make a linear spiral, which wasn't possible with the spiral tool. But I found the workaround to the issue.
That spiral is called Archimedean Spiral. True, there are only work arounds how to create these in Illustrator.
They are so easy to create in Inkscape!
It’s been on the wish list for many years now. No avail.
Here are two such Links.