WFM schedule group 400 via Terraform

Why does this setting fail with a 400 error?

Provider v1.68.4. Region au-1.

The HCL validates but the API rejects the shift_pattern field.

resource “genesyscloud_wfm_schedulegroup” “test” {
name = “Test”
shift_pattern_id = data.genesyscloud_wfm_shiftpattern.main.id
}

Error: Invalid shift pattern reference.