Fix compile errors

backend/src/api.rs

@@ -5,7 +5,7 @@ use axum::{
     extract::{Path, State},
     http::{HeaderMap, Method, StatusCode, Uri},
     response::{IntoResponse, Response},
-    routing::{delete, get, post, put},
+    routing::{get, put},
     Json, Router,
 };
 use serde::{Deserialize, Serialize};
@@ -325,7 +325,7 @@ async fn list_tenant_invoices(
     }
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Deserialize, Serialize)]
 struct UpdateTenantBillingRequest {
     tenant_nwc_url: String,
 }