Hello @bigbacon ,

Validate the URL also check the roles for .NET user in servicenow to read /write/create hr case.

Please steps in servicenow to validate url and fields for rest integration can use for troubleshoot 

1. Navigate rest api explore in your ServiceNow instance

2. Select table api

3.retrive a record [get]

4.add details as "sn_hr_core_case" and sys_id of record to extract which need s extract and check 200 response.

Supriya Waghmode |ServiceNow Consultant