diff --git a/src/index.ts b/src/index.ts
index a41be0e..6a0bc85 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -108,7 +108,7 @@ app.post("/messages/:id/ack", requireWebAuth, async (req, res) => {
   const identity = String(
     user.preferred_username ?? user.email ?? user.name ?? user.sub ?? "web-user"
   );
-  await acknowledgeAgentMessage(req.params.id, `web:${identity}`);
+  await acknowledgeAgentMessage(String(req.params.id), `web:${identity}`);
   return res.redirect("/");
 });