diff --git a/src/app/api/whatsapp/webhook/route.ts b/src/app/api/whatsapp/webhook/route.ts
index ba404f8..aff9761 100644
--- a/src/app/api/whatsapp/webhook/route.ts
+++ b/src/app/api/whatsapp/webhook/route.ts
@@ -1,4 +1,4 @@
-import { NextResponse } from 'next/server'
+import { NextResponse, after } from 'next/server'
 import { createClient } from '@supabase/supabase-js'
 import { decrypt, encrypt, isLegacyFormat } from '@/lib/whatsapp/encryption'
 import { getMediaUrl, downloadMedia } from '@/lib/whatsapp/meta-api'
@@ -12,6 +12,12 @@ import {
   isTemplateWebhookField,
 } from '@/lib/whatsapp/template-webhook'
 
+// The `after()` callback in POST runs within this route's max duration.
+// Inbound processing can fan out to per-media Meta verification calls, so
+// give it headroom beyond the platform default (Vercel clamps this to the
+// plan's ceiling). Tune as needed.
+export const maxDuration = 60
+
 // Lazy-initialized to avoid build-time crash when env vars are missing
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 let _adminClient: any = null
@@ -182,9 +188,26 @@ export async function POST(request: Request) {
     return NextResponse.json({ error: 'Invalid JSON' }, { status: 400 })
   }
 
-  // Process asynchronously so we can ack Meta within their timeout.
-  processWebhook(body).catch((error) => {
-    console.error('Error processing webhook:', error)
+  // Process AFTER the response so we ack Meta within their ~20s timeout
+  // (a slow ack triggers Meta retries + duplicate inserts), while still
+  // guaranteeing the work runs to completion.
+  //
+  // This MUST use `after()` rather than a detached `processWebhook(body)`
+  // promise: on serverless platforms (we run on Vercel) the function can
+  // be frozen or terminated the moment the response is sent, so a floating
+  // promise's DB writes are not guaranteed to finish. That dropped a
+  // non-deterministic *subset* of inbound messages — contacts/conversations
+  // were created but the message insert never landed, leaving conversations
+  // that show in the inbox with an empty thread, and no logs to explain it
+  // (see issue #301). `after()` hands the callback to the runtime, which
+  // keeps the function alive until it resolves (within the route's
+  // maxDuration).
+  after(async () => {
+    try {
+      await processWebhook(body)
+    } catch (error) {
+      console.error('Error processing webhook:', error)
+    }
   })
 
   return NextResponse.json({ status: 'received' }, { status: 200 })