OData GET Returning ODP_RESOURCE_NOTFOUND

I’m building a custom external integration for IFS Cloud, using the OData REST APIs. I have some projections that seem to be working fine, for example, if I specify a valid CustomerId to this endpoint, https://<our-cloud-url>/main/ifsapplications/projection/v1/CustomersHandling.svc/CustomerInfoSet(CustomerId='VALID-ID'), I get valid data back. However, I have some projections that are always returning ODP_RESOURCE_NOTFOUND. For example, I’ve tried a variety of ways to get the data for a Shipment. https://<our-cloud-url>/main/ifsapplications/projection/v1/ShipmentHandling.svc/ShipmentSet(ShipmentId=1) and https://<our-cloud-url>/main/ifsapplications/projection/v1/ShipmentsHandling.svc/Reference_Shipment(ShipmentId=1), even tried getting the overview list of shipments using https://<our-cloud-url>/main/ifsapplications/projection/v1/ShipmentsHandling.svc/OverviewShipmentSet, but that returns this:

{
  "@odata.context": "https://<our-cloud-url>/main/ifsapplications/projection/v1/ShipmentsHandling.svc/$metadata#OverviewShipmentSet",
  "value": []
}

These are the same projections that the aurena client is using, so I’m thinking that my IAM Client maybe has a configuration / permissions problem? Any tips on how to troubleshoot this?

FWIW - I switched my OAuth token request to be a user+password scheme using my IFS user account. Doing this, all the expected endpoints are working. Therefore it does seem this is some kind of permissions issue with the service account I created, I’m just not sure how to resolve it.