Genesyscloud_ivr_script 400 on external file ref

Configuration is broken for some reason…

Context:
env: us-1 prod
provider: genesys 1.15.4
tf: 1.6.5
resource: genesyscloud_ivr_script
the error is
POST /api/v2/flow/ivrs/scripts returns 400 Bad Request

resource “genesyscloud_ivr_script” “test” {
name = “Test Script”
script_type = “EXTERNAL”
external_script_url = “https://example.com/script.json
}

Question:
Why does setting script_type to EXTERNAL trigger 400? The URL is valid. Is external scripting disabled for IVR in current API version?