POST /api/v2/outbound/contacts/lists returns 400 INVALID_VALUE

Trying to create a new contact list via the REST API. Getting a 400 Bad Request with INVALID_VALUE on the name field. The docs say it needs to be a string, which it is.

Here’s the payload:

{
 "name": "Test List 1",
 "description": "Automated test",
 "contactFields": [
 {
 "id": "phone_number",
 "label": "Phone",
 "type": "string"
 }
 ]
}

Checked the token. It’s valid. Tried POSTing to /api/v2/outbound/contacts/lists with Content-Type: application/json. Same error.

Tried changing the name to something simpler. No luck. Tried removing the description. Still fails. The error message is generic. Doesn’t say which value is invalid, just that one is.

scripts handle this differently, but I need this in Python for a batch process. The SDK method create_contact_list wraps this endpoint. Same result.

Is there a hidden constraint on the name? Regex? Special chars? The name is plain text.

Logs show the request hits the server. Response is immediate. No timeout.

Any ideas?