pmm-admin is confused by HTTP server URL

root@ip-10-1-2-184:~# pmm-admin config --server-url=http://127.0.0.1:80
Checking local pmm-agent status...
pmm-agent is running.
Registering pmm-agent on PMM Server...
Failed to register pmm-agent on PMM Server: Post https://127.0.0.1:80/v0/management/Node/Register: http: server gave HTTP response to HTTPS client.