status code changes

We will be releasing a change to this service to provide more consistent status codes for error situations.

Currently the service will return a 500 status for a range of conditions. Many of these are due to problems reaching the underlying product instance. This can be due to situations such as the instance being suspended, etc.

These situations will now report as a 502 indicating that the problem is with the upstream service rather than the service itself.

Currently there are some circumstances where the service will return a 400 status which is misleading. These will also now return a 502 status