'GCP Load Balancer non-www to www redirect

I'm following this guide https://cloud.google.com/load-balancing/docs/https/setting-up-http-https-redirect#console_6 to setup non-www to www redirect on Google Cloud Load Balancer. But when I try to assign the same IP to non-https load balancer I get this error

Invalid value for field 'resource.IPAddress': 'projects/serpworx-node-live/global/addresses/my-project'. Specified IP address is in-use and would result in a conflict.



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