Please upload a debug log and post just the token URL that is generated after the log is uploaded by running the following command from the Pi-hole host terminal:
Was this really shown as an error to you? This log line might be created during internal config file migration but should only have significance INFO. I will open a PR that moves this into DEBUG realm as there is no issue at all with this message. It simply means your config wasn't old - meaning it didn't need migration.
Indeed, dns,revServer (one setting) became dns.revServers (an array) to support multiple conditional forwarding servers.