WFM API 400 on Skill Assignment via CX as Code

Just noticed that the WFM API returns a 400 Bad Request when assigning skills to users via our Terraform wrapper. The endpoint /api/v2/wfm/users/{userId}/assignments rejects the payload below.

{
 "skillAssignments": [
 {
 "skillId": "83746-1234-5678",
 "level": 3,
 "effectiveDate": "2023-11-01T00:00:00Z"
 }
 ]
}

Provider v1.92.0, US East. Error says skillId is invalid, but it exists in the org. Is this a known schema drift issue?