TMF622 ProductOrdering, how the productSpecification.href is used in the (POST) request? does if filled automatically or manually in the request? can we do a POST request without it?
As a general rule, I don't think it's reasonable to expect that href will be populated in any POST/PATCH operation call on input (i.e. request). The href is useful in output so that the consumer can directly link to the created/updated entity.
It's the responsibility of the API implementation to populate in the response body. Bear in mind that transformations may need to be done on the raw output URL due to API gateways, redirections, and more.
Hope it helps