How to enable Custom Planning Source System for REST calls?

There is a requirement for applying credit check hold on sales orders using REST API. Code is working fine on sales orders created manually. But, it is not working on the sales orders which were created using FBDI. We are using custom Planning Source System for these orders. Is there a setup where we can enable this system for REST calls? We are getting below error for such orders.

<result>
<RequestStatus>ERROR</RequestStatus>
<Message>An error occurred: Cannot invoke "java.util.List.size()" because the return value of "oracle.apps.scm.doo.common.holds.model.HoldRequest.getSubRequests()" is null. Contact your help desk. (DOO-2685513) An application error has occurred. Your help desk can use the