The [12.0.1 release](
https://github.com/davidtsadler/ebay-sdk-php/releases/tag/12.0.1) of the PHP SDK will handle this situation better. It will now ignore any properties in the JSON response that it is unaware off. It means that I will have time to read the documentation regarding any API updates and then implement it. Should hopefully stop people's projects from breaking while they wait for the SDK to be updated.