Flashbots protect rpc conecting to a trusted builder

Is it possible to connect flashbots protect rpc to a known builder? I bult protect rpc on my mac and tried to run it. I set, export PROXY_URL=“”, builder is running on the port 8545. However, go run cmd/server/main.go -redis dev -signingKey dev -proxy PROXY_URL gives an error: Server init error error=“fetchNetworkIDBytes error: cl.NetworkID error: Post "PROXY_URL": unsupported protocol scheme ""”