WFM API 403: Zendesk Agent Group to Genesys Cloud Business Unit Mapping

Anyone free to help troubleshoot this 403 Forbidden error when mapping Zendesk agent groups to Genesys Cloud Business Units via the POST /api/v2/wfm/schedules endpoint. The migration script uses the genesyscloud-python SDK v12.1.0 and fails specifically on the business_unit_id field, whereas direct Zendesk group IDs work fine in the source system. Environment is Genesys Cloud Public (EU-West) and the user has wfm:schedule:write permissions.