diff --git a/pkg/cmd/services.go b/pkg/cmd/services.go
index d770863..6761efd 100644
--- a/pkg/cmd/services.go
+++ b/pkg/cmd/services.go
@@ -129,8 +129,8 @@ var servicesCancelCmd = cli.Command{
 	Usage:     "Cancel a service",
 	ArgsUsage: "<service-id>",
 	Flags: []cli.Flag{
-		&cli.StringFlag{Name: "reason", Usage: "Cancellation reason", Required: true},
-		&cli.StringFlag{Name: "reason-detail", Usage: "Cancellation reason detail"},
+		&cli.StringFlag{Name: "reason", Usage: "Cancellation reason code (see services cancellation-reasons)", Required: true},
+		&cli.StringFlag{Name: "reason-detail", Usage: "Cancellation reason text (required for CANCEL_OTHER)"},
 	},
 	Action:          handleServicesCancel,
 	HideHelpCommand: true,
@@ -146,10 +146,10 @@ func handleServicesCancel(ctx context.Context, cmd *cli.Command) error {
 		return err
 	}
 	payload := map[string]string{
-		"reason": cmd.String("reason"),
+		"reasonCode": cmd.String("reason"),
 	}
 	if d := cmd.String("reason-detail"); d != "" {
-		payload["reasonDetail"] = d
+		payload["reason"] = d
 	}
 	body, _ := json.Marshal(payload)
 	_, err = client.PostJSON(ctx, "/services/v1/services/"+args[0]+"/cancel", body)
diff --git a/pkg/cmd/services_test.go b/pkg/cmd/services_test.go
new file mode 100644
index 0000000..c9fb026
--- /dev/null
+++ b/pkg/cmd/services_test.go
@@ -0,0 +1,59 @@
+package cmd
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestServicesCancel(t *testing.T) {
+	for _, test := range []struct {
+		name    string
+		reason  string
+		detail  string
+		payload map[string]string
+	}{
+		{
+			name:   "predefined reason",
+			reason: "CANCEL_PRODUCT_SWITCH",
+			payload: map[string]string{
+				"reasonCode": "CANCEL_PRODUCT_SWITCH",
+			},
+		},
+		{
+			name:   "other reason with detail",
+			reason: "CANCEL_OTHER",
+			detail: "Do not renew at the end of the current contract term.",
+			payload: map[string]string{
+				"reasonCode": "CANCEL_OTHER",
+				"reason":     "Do not renew at the end of the current contract term.",
+			},
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			called := false
+			srv := newTestServer(t, map[string]http.HandlerFunc{
+				"POST /services/v1/services/12345/cancel": func(w http.ResponseWriter, r *http.Request) {
+					called = true
+					var payload map[string]string
+					require.NoError(t, json.NewDecoder(r.Body).Decode(&payload))
+					assert.Equal(t, test.payload, payload)
+					w.WriteHeader(http.StatusNoContent)
+				},
+			})
+			defer srv.Close()
+
+			args := []string{"services", "cancel", "12345", "--reason", test.reason}
+			if test.detail != "" {
+				args = append(args, "--reason-detail", test.detail)
+			}
+			_, stderr, err := runCLI(t, srv.URL, args)
+			require.NoError(t, err)
+			assert.True(t, called)
+			assert.Contains(t, stderr, "Cancelled service 12345")
+		})
+	}
+}