Setup each proxy as it's own proxy network for VotingPlugin before setting multi-proxy up, each proxy can use a different proxy method
Note if using REDIS (Not for multi-proxy method) you will need to set a different redis prefix for each proxy network (This is so that all proxies can use REDIS at the same time without issue)
Check connection status with /votingpluginbungee multiproxystatus - should see a message on each proxy in console