You have run a script to configure a new VLAN on a CX switch, but...

When receiving a '404 - Not Found' HTTP response while attempting to configure a VLAN via REST API, the most common cause is specifying an incorrect URI endpoint. The correct approach is to specify the exact resource path for VLAN configuration, which is /rest/v1/system/vlan. Without the correct URI, the API will return a 404 error indicating the resource is not found.

Sending a POST request to login is necessary but not related to 404 after login.

Syntax errors in payload lead to 400-series errors but usually not 404.

Enabling REST API read/write is important but would result in different errors.