A few years late, but in case someone finds this thread: You can now provision NAT IPs for a static IP address(es): https://cloud.google.com/apigee/docs/api-platform/security/nat-provisioning

I ran into a similar issue where substring was unexpectedly returning empty string. Setting IgnoreUnresolvedVariables AND removing the space after the comma resolved it. {substring(request.header.authorization,7)} Removing only space without IgnoreUn...