Comment 3 for bug 1848880

The fact that there is no oem-config-prepare / OEM mode on the live-server image is a known thing; I don't think that has been implemented at all in subiquity yet.

However, you really should have has oem-config-prepare available at the end of an OEM install from the server image; I'll investigate why that wasn't the case, first by trying to reproduce the issue.