Not quite sure this is the best spot for this question but I will start here. I am trying to create a custom record that is the child of the Inbound Shipment record. I am unable to check the 'Record is Parent' checkbox when adding the Inbound Shipment field to my custom record, is there a setting needed to allow for making the Inbound Shipment a parent records, or are some records just not able to be parent records?

That's pretty curious, wonder what would be the point in that architecture.

Right, the record is also available as its own record type and from the transaction table so I am not sure which to use