Thanks for the info. Yes, I see that flatpak is trying to download the deb file for the 32-bit Spotify client from the Spotify repos. I tried to download it directly using curl but it failed. It sure looks like the .deb file is corrupt or perhaps the permissions are set incorrectly.
I have reported the problem to the Spotify Community Forums.
See
I am hoping Spotify will fix the corrupt .deb file or at least inform me that it no longer develops and supports the 32-bit Spotify client.