Notes from the field: vCenter cannot validate SSO domain

Came across a peculiar issue when adding an second vCenter to the same SSO domain and enable ELM.
The first deployment worked like a charm and the second errored out with the following error:

It turns out there is a known bug when using uppercase FQDN in the configuration wizard, the solution is to put it all in lowercase.
see the following link for reference: https://kb.vmware.com/s/article/56812