Retrieve all the subprocesses given the process instance of a parent workflow

I would like to know if there’s a REST API that provides a list of subprocesses that are active and got triggered/called from a parent workflow, for which i already have the processInstanceId.

I’m following this POST rest api here and tried adding ‘subProcessInstance’ as my parent id but it’s returning an empty list but i see there’s a subprocess currently active and waiting that got called in this parent workflow.

Rest API: Get Instances (POST) | docs.camunda.org

url: https://localhost:8080/engine-rest/process-instance
body:
{
“processDefinitionKey”: “demoParentWorkflow”,
“subProcessInstance”: “9218”, // subprocesses should belong to this process instance id
“active”: true
}