The error is logged in the following files:
YYYY-MM-DDTHH:MM:SS.337Z INFO domain_consolidator validating saml tokenYYYY-MM-DDTHH:MM:SS.338Z ERROR domain_consolidator Failed to validate sso credentials. Error <urlopen error timed out>Source Platform Services Controller details provided are incorrect. Check the credentialsYYYY-MM-DDTHH:MM:SS.339Z INFO domain_consolidator Invalid user input entered.
YYYY-MM-DDTHH:MM:SS.337Z INFO cmsso_util Error in retrieving appliance type of server vcenter.example.com: HTTPSConnectionPool(host='vcenter.example.com', port=443): Max retries exceeded with url: /rest/vcenter/system-config/deployment-type (Caused by ProxyError('Cannot connect to proxy.', OSError('Tunnel connection failed: 504 Gateway Timeout'))).
vCenter Server 7.0.x
vCenter Server 8.0.x
NOTE: Ensure to take a no memory snapshot of the vCenter server if it is standalone or powered off snapshots of all vCenter servers if they are in linked mode before the above process
https://techdocs.broadcom.com/us/en/vmware-cis/vsphere/vsphere/7-0/vcenter-installation-and-setup/after-you-install-vcenter-server/repoint-vcenter-server-to-another-vcenter-server-in-a-different-domain/repoint-to-an-existing-embedded-domain.html
https://techdocs.broadcom.com/us/en/vmware-cis/vsphere/vsphere/7-0/vcenter-installation-and-setup/after-you-install-vcenter-server/repoint-vcenter-server-to-another-vcenter-server-in-a-different-domain/repoint-an-embedded-node-to-a-new-domain.html