Do you have a sample payload you used for creating the directory? Not sure what goes in the directoryConfig object.
{
"directoryConfig": {},
"directoryType": "ActiveDirectory",
"vidmAdminPassword": "some-password",
"vidmAdminUser": "configadmin",
"vidmHost": "vidm.corp.local,
"vidmTenant": "default",
"vidmVersion": "3.3.5"
}