fix: resolve missing API_URL and refactor payment portal call

apps/admin/src/pages/SettingsPage.tsx

@@ -227,22 +227,11 @@ export default function SettingsPage() {
                         <button 
                             onClick={async () => {
                                 try {
-                                    const apiKey = localStorage.getItem('edtech_admin_key');
-                                    const res = await fetch(`${API_URL}/v1/payments/customer-portal`, {
-                                        method: 'POST',
-                                        headers: { 
-                                            'Authorization': `Bearer ${apiKey}`,
-                                            'x-organization-id': selectedOrgId!
-                                        }
-                                    });
-                                    if (res.ok) {
-                                        const { url } = await res.json();
-                                        window.location.href = url;
-                                    } else {
-                                        alert('Impossible d\'ouvrir le portail de facturation.');
-                                    }
+                                    const { url } = await api.post('/v1/payments/customer-portal', {}, token, selectedOrgId);
+                                    window.location.href = url;
                                 } catch (err) {
                                     console.error(err);
+                                    alert('Impossible d\'ouvrir le portail de facturation.');
                                 }
                             }}
                             className="w-full py-3 bg-indigo-600 text-white rounded-xl font-bold hover:bg-indigo-700 transition-all flex items-center justify-center gap-2"