Script node POST returning 400 on custom field mapping

The script editor throws a 400 Bad Request when binding a custom field to a set variable node. Request body looks standard enough, yet validation keeps blocking deployment. Cleared cache and swapped to a fresh script template, but the payload rejects the reference every time. Logs timestamped 02:14 PDT show POST /api/v2/scripting/script-nodes/definitions failing with "error": "Invalid field reference: custom_field_9921 does not match schema". Running Genesys Cloud 2024-10 build on us-west-2 edge. Field exists in org settings and passes contact object validation. Architect flows pulling the same identifier via contact.custom_field_9921 work fine. Routing layer isn’t the bottleneck. Doing jack all with the UI layout since the queue analytics dashboard won’t refresh until the script version publishes.

{
 "type": "setVariable",
 "data": {
 "variableName": "complaintCode",
 "value": {
 "type": "field",
 "fieldId": "custom_field_9921"
 }
 }
}