POST /api/v2/outbound/contactlists returns 400 INVALID_VALUE on name field

Trying to spin up a new Outbound contact list via the REST API for our custom agent desktop integration. The payload looks standard, but the server keeps rejecting it with a 400 error.

Here’s the JSON I’m sending:

{
 "name": "Campaign_List_Oct",
 "type": "CONTACT",
 "contactCenterId": "my-cc-id",
 "columns": [
 {
 "name": "phone",
 "type": "PHONE",
 "required": true
 }
 ]
}

The error response is:

{
 "message": "The request entity is invalid.",
 "status": 400,
 "code": "invalid_value",
 "errors": [
 {
 "message": "The value is not valid.",
 "path": "name"
 }
 ]
}

I’ve verified the contactCenterId is correct and the auth token has outbound:contact:list:write permissions. Renaming the list to something simpler like “TestList” didn’t help. Even removing the columns array leaves me with the same invalid_value on the name field.

Is there a hidden format requirement for the name string? Or maybe a character limit I’m missing? The docs don’t specify anything beyond it being a string. Tried escaping spaces, changing case, nothing works.