"503 Service Unavailable" error on the vSphere Web Client ...
kb.vmware.com › s › articleMay 18, 2021 · The vCenter server was able to process your request and was able to respond back with the " 503 Service Unavailable " error. It is just not able to acknowledge your request either because it is busy with other tasks at the moment or it currently down with very limited services due to maintenance. Try again in a few minutes on a different client.