Server 5.17 download

I was able to download 5.0.15 server app from the App Store purchased Tab while logged into an apple id which had previously purchased Server. App Store indicated that the current version I had was not compatible but let me have 5.0.15 as the latest known compatible version for the macOS version installed.

Once I had 5.0.15 this put me on a supported upgrade path. (Upgrade and migrate data on your macOS Server - Apple Support) I upgraded from there to Sierra and it detected an out of date server, disabled it, and offered me 5.2. All my data migrated smoothly. I talked this approach through with Apple Enterprise Support and tested it on a backup system before updating the live customer server.

This was a couple of weeks ago. High Sierra has since come out so things may well have changed now.

App Store should offer you the latest compatible version of Server.app for the OS that is installed.

You may have to delete any existing Server.app on the filesystem for it to show up in the purchased tab.

I updated my Xserve 3,1's to Sierra using a widely available patch, but I dont use server.app on them.

The computers I was installing Server on for my client were Mac Pro 2013's so I didnt see this issue.

Being offered an incompatible version is a bug though. I can only suggest reporting it to Apple Enterprise Support. I dont think they ever read these forums.