Try changing from this:
"parentLocation" : {
"uuid": "8d6c993e-c2cc-11de-8d13-0010c6dffd0f"
}
to this:
"parentLocation" : "8d6c993e-c2cc-11de-8d13-0010c6dffd0f"
(The underlying REST API doesn’t properly support letting you post back objects instead of just UUIDs. In some cases you can do this, but in many cases it doesn’t work.)