External PSC upgrade error 6.0 -> 6.5 - Installer can't determine source PSC/SSO version

Hi Colleagues,

I'm trying to update my infrastructure from 6.0 to 6.5.

I have the latest build (5202501) of external PSC 6.0:

External PSC health is Good. Auth is working fine, i don't see anomalies in PSC functionality:

I'm filling in all required source information about PSC and source vCenter/ESXi:

But installer can't determine version of source appliance:

Any ideas why is it happening happening and how to solve it?  May be i should change something in source appliance.

I tried to continue installation, but anyway it's failed as source version is incorrect.

Thank you in advance!