ZCS 8 to ZCS 8, "Start Migration" button MIA

I am mtrying to move from one old machine to a new one, but I have upgraded the old Zimbra to version 8 first, so both servers have the same Zimbra version.

Unfortunately, The "Start Migration" button is nowhere to be found.
According to Zx Backup: Migration Tool Export - ZeXtras Suite Wiki , it should be at the header, but it's just not there.
I have looked around the interface, but haven't seen it at all.
ZxExtras version is 1.6.0, the latest one.

Any help here? Thanks