Posting a Change request using Admin API fails when the approver is specified

Issue

Using Admin REST API, when submitting a change request doc link here, and specifying the approver contact, the request fails with 400 error

{"code":400,"message":"Something was wrong","details":"","transactionId":"xxxxxxx"}

Root Cause

This error is possible if the approver option is set in the Environment that has the Split, when the approvers are pre-selected, it is not allowed to specify an approver when submitting the change request, similar to when submitting the change from Split UI, the approver edit box will be greyed out.

Answer

Verify if the Split definitions belong to an Environment that has approvers set in it's permissions, if so, remove the approver contact and leave the approvers array empty in the JSON payload

"approvers":[]