Gov-Client-Public-IP and Gov-Vendor-Forwarded fraud prevention headers don't support hybrid IPv4/IPv6 addresses about vat-api

[DigitalDan1]

The Software Developer Support Team have been very helpful. We eventually worked out what the problem was. Here's their response:

We can confirm the validation rules support processing of IPv4-mapped IPv6 addresses. This is why the error message states "not a public IP address" instead of an invalid IP address.

We believe we started seeing invalid fraud headers after some updates to our hosting environment, then incorrectly assumed the error was due to the change in formatting of the IP address, but we'd actually broken the way we determine the public IP address of the client. After fixing that the headers are valid.