This assumes you have used the curl REST API to obtain an OAuth bearer token. Let's say the bearer token is sha256~0Rs__hPuXmBD3TJTXNDisC7wRBN-nrFnYTxgdBrFT-U.

Here is how you would list the services in the "default" namespace using the curl REST API. The oc config view or oc get apiserver commands can be used to display the API Server URL (api.openshift.example.com in this example).

curl
--insecure
--request GET
--header "Accept: application/json"
--header "Authorization: Bearer sha256~0Rs__hPuXmBD3TJTXNDisC7wRBN-nrFnYTxgdBrFT-U"
--url "https://api.openshift.example.com:6443/api/v1/namespaces/default/services"

If something like this is returned, this means that there are no services in the namespace.

{
  "kind": "ServiceList",
  "apiVersion": "v1",
  "metadata": {
    "selfLink": "/api/v1/namespaces/default/services",
    "resourceVersion": "136867665"
  },
  "items": []
}

On the other hand, if the items array contains key value pairs, this means the namespace contains one or more services.

{
  "kind": "ServiceList",
  "apiVersion": "v1",
  "metadata": {
    "selfLink": "/api/v1/namespaces/default/services",
    "resourceVersion": "136864373"
  },
  "items": [
    {
      "metadata": {
        "name": "example-service",
        "namespace": "default",
        "selfLink": "/api/v1/namespaces/default/services/example-service",
        "uid": "80447653-07a2-449f-9570-1199fb5385c9",
        "resourceVersion": "202",
        "creationTimestamp": "2021-07-16T17:09:51Z",
        "annotations": {
          "prometheus.io/port": "9542"
        },
        "labels": {
          "component": "apiserver",
          "provider": "example-service"
        },
        "managedFields": [
          {
            "manager": "kube-apiserver",
            "operation": "Update",
            "apiVersion": "v1",
            "time": "2021-07-16T17:09:51Z",
            "fieldsType": "FieldsV1",
            "fieldsV1": {"f:metadata":{"f:labels":{".":{},"f:component":{},"f:provider":{}}},"f:spec":{"f:clusterIP":{},"f:ports":{".":{},"k:{\"port\":443,\"protocol\":\"TCP\"}":{".":{},"f:name":{},"f:port":{},"f:protocol":{},"f:targetPort":{}}},"f:sessionAffinity":{},"f:type":{}}}
          }
        ]
      },
      "spec": {
        "ports": [
          {
            "name": "https",
            "protocol": "TCP",
            "port": 443,
            "targetPort": 6443
          }
        ],
        "clusterIP": "172.30.0.1",
        "type": "ClusterIP",
        "sessionAffinity": "None"
      },
      "status": {
        "loadBalancer": {
          
        }
      }
    }
  ]
}

Or to return a specific service, such as example-service.

curl
--insecure
--request GET
--header "Accept: application/json"
--header "Authorization: Bearer sha256~0Rs__hPuXmBD3TJTXNDisC7wRBN-nrFnYTxgdBrFT-U"
--url "https://api.openshift.example.com:6443/api/v1/namespaces/default/services/example-service"