Kiali UI not showing API Docs tab

Question

I'm trying to get Kiali to show my swagger docs in the UI but it doesn't.

Here is the service definition

% kubectl describe service/plans-api --namespace plans --context dd-stag
Name:              plans-api
Namespace:         plans
Labels:            repository=plans
                   service=plans-api
                   skaffold.dev/run-id=x
Annotations:       kiali.io/api-spec: http://plans-api.plans/swagger/doc.json
                   kiali.kubernetes.io/api-type: rest
Selector:          app=plans-api,repository=plans,service=plans-api
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                172.16.21.55
IPs:               172.16.21.55
Port:              plans-api  80/TCP
TargetPort:        8080/TCP
Endpoints:         172.20.1.131:8080
Session Affinity:  None
Events:            <none>

then, this is what I get. See that API Docs tab is not showing:

Scraping a bit with the inspector, I can see that the annotation for the service is in place:

{
{
    "service": {
        "name": "plans-api",
        "createdAt": "2023-09-26T07:40:16Z",
        "resourceVersion": "447498536",
        "namespace": {
            "name": "plans",
            "cluster": "",
            "isAmbient": false,
            "labels": null,
            "annotations": null
        },
        "labels": {
            "repository": "plans",
            "service": "plans-api",
            "skaffold.dev/run-id": "x"
        },
        "selectors": {
            "app": "plans-api",
            "repository": "plans",
            "service": "plans-api"
        },
        "type": "ClusterIP",
        "ip": "172.16.21.55",
        "ports": [
            {
                "name": "plans-api",
                "protocol": "TCP",
                "istioProtocol": "UnsupportedProtocol",
                "port": 80,
                "tlsMode": "istio"
            }
        ],
        "externalName": "",
        "annotations": {
            "kiali.io/api-spec": "http://plans-api.plans/swagger/doc.json", // <- 
            "kiali.kubernetes.io/api-type": "rest", // <-
            "kubectl.kubernetes.io/last-applied-configuration": "x"
        },
        "healthAnnotations": {},
        "additionalDetails": []
    },
    ...
}

I'm unsure if it is a bug or a misconfiguration from my side. Any help is appreciated :)