Hi, As part of out of box cases api, external system can trigger a create case and receives the case id created.  When the workflow supports, parent case and child case creation, how external system can get the child case id immediately. 

Figured out below options and made some workaround, but is there any way we can do without any configuration/ootb behaviour change. API Used: https://xx/prweb/api/v1/cases 1. Ask external system to create a case first and use the case id to retrieve the case id using Get Cases API to get the child case id (not preferred one for quicker response time)

2. Create a new flow in the respective case type and call the pyStartCase flow as subprocess and use utility to open the child case id using pxCoveredInsKey(<LAST>) which sends the child case id by default.  (this workaround suits the requirement)