All error codes

router_interface_not_found

HTTP 409 The router has no interface with this name

What happened

The router has no interface with the name you gave. Only ethernet interfaces of the router (eth0, eth1, ...) can be named in a rule.

What to do

Read GET /v1/servers/{id}/router/networks for the interface names this router has, then repeat with one of them - or with null to match any interface.

Retrying

Change the state this refers to, then repeat the same request with the same idempotency key.

How it arrives

{
    "type": "https://docs.fiberax.com/errors/router_interface_not_found",
    "title": "The router has no interface with this name",
    "status": 409,
    "code": "router_interface_not_found",
    "request_id": "a277dcd1ca652c65"
}

Branch your code on code, never on the wording of title.