You are writing a Python script using the requests library to push an OSPF area configuration to an IOS-XE device via RESTCONF. When the device rejects a malformed payload, it returns an HTTP 400 status. Your operations team needs the script to log the specific reason for the failure (such as which leaf failed validation) so they can troubleshoot without opening the device. Where in the HTTP response should your code look to extract this structured error detail?