Line messager show "A timeout occurred when sending a webhook event object" error

Spaces
4

Hmm… I’ve never used the N8N, so I don’t know much about it.

The message

“A timeout occurred when sending a webhook event object”

means: LINE tried to POST a webhook to your bot server, but did not get a valid HTTP 2xx response fast enough or at all. Everything else is details.

I’ll walk through:

  1. What LINE’s backend is actually doing
  2. Common technical causes (grouped)
  3. Solutions and design patterns, with n8n / Hugging Face context in mind

1. What LINE expects from your webhook

From LINE’s official docs, every webhook delivery ends in one of a few categories: (LINE Developers)

  • could_not_connect
    LINE could not connect to your server at all
    (DNS failure, TCP connect timeout, TLS handshake failure, invalid URL, etc.)

  • request_timeout
    LINE connected and sent the request, but your server didn’t return a response within ~2 seconds.

  • error_status_code
    LINE got a response but it was not 2xx (e.g. 400 / 404 / 500 / 502 / 503).

The user-facing console often just shows something like:

“A timeout occurred when sending a webhook event object”

but under the hood it’s one of those reasons. For your case that usually means request_timeout or an error_status_code that the console is simplifying. (LINE Developers)

So your bot server must:

  1. Accept HTTPS POST from LINE.
  2. Return HTTP 200–299.
  3. Do it very quickly (within about 2 seconds).

If you miss any of these, you get that error.

2. Typical causes in practice

I’ll group causes into three big buckets.

2.1 Server unreachable (could_not_connect)

Symptoms:

  • No request appears in your app logs.
  • LINE console: timeout error; error statistics show could_not_connect. (LINE Developers)

Common reasons:

  1. Wrong URL or path

    • Example: LINE URL is https://example.com/callback, but your app exposes /line/callback.
    • You see 404 in your own logs or in a tunnel like ngrok; users report exactly this with that same timeout message + 502/404 in ngrok. (Learn Code With Mike)

  2. Wrong port or service not running

    • Tunnel pointing at port 8000 while the server listens on 5000.
    • Container not started yet, or crashed, so reverse proxy returns 502.

  3. TLS / HTTPS mismatch

    • Using HTTP on port 80 with a URL that starts with https://.
    • Certificate chains or TLS versions not compatible with LINE’s webhook spec (there are docs about acceptable TLS). (LINE Developers)

  4. Network and firewall

    • Local firewall or corporate proxy blocking inbound requests from LINE.
    • Router / modem issues; some users have literally fixed the timeout by rebooting their router and PC, with no code changes. (Facebook)

2.2 Server reachable but too slow (request_timeout)

Here LINE does connect and send the POST, but does not get a response in time. Official docs:

“LINE platform sent a webhook to the bot server, but did not receive a response within a certain period (around 2 seconds).” (LINE Developers)

Common causes:

  1. Long-running logic in the webhook handler

    • Doing slow tasks inline:

      • Calling external APIs (LLMs, other Spaces, DBs).
      • Generating images or running heavy ML models.
      • Writing to spreadsheets or remote storage.

    • Google Apps Script + LINE tutorials hit this exact problem; they see the same timeout error when writing to Sheets inside the webhook call. (Hugging Face Forums)

  2. Cold start on serverless / PaaS platforms

    • On platforms like Hugging Face Spaces, if the app slept, the first request wakes the container and starts the app.
    • Reports show cold boot can take tens of seconds or longer, well beyond LINE’s 2-second window. (Hugging Face Forums)

  3. Heavy payloads and slow parsing

    • n8n users see 408 / timeout even with simple Webhook → Respond to Webhook flows when huge payloads arrive (e.g., big WhatsApp broadcasts). (n8n Community)

  4. Webhook frameworks waiting for the whole workflow

    • In tools like n8n, a webhook node by default might wait for the entire workflow to complete before sending the HTTP response.
    • If the workflow is slow, the initial request times out. Community threads confirm n8n has its own timeout (on the order of 1–2 minutes); external services with shorter limits will see timeouts well before that. (n8n Community)

Result: LINE times out even if your code eventually finishes. You might even see your bot reply “late” in chats while the console still shows timeout errors.

2.3 Server responds with non-2xx (error_status_code)

Here LINE does get a response, but it is not 2xx. Officially: (LINE Developers)

“Your server returned a response whose HTTP status code is not in the 200 range.”

Typical examples:

  1. 404 / 405

    • Wrong HTTP method (GET vs POST).
    • Wrong path mapping in your framework.
    • Common with Flask/Django or when the callback route has a prefix that was not included in the webhook URL. Bloggers documenting that same “timeout” error often show 404/502 in ngrok logs. (Learn Code With Mike)

  2. 500 / 502 / 503

    • Unhandled exceptions in the code.
    • Upstream dependency failure (e.g., your app calls another API that 500s, you bubble that up).
    • Reverse proxy returns 502 because the backend process crashed or never bound to the expected port. Hugging Face Spaces posts show “space was not healthy / stuck in building / starting” leading to these errors. (Hugging Face Forums)

  3. 302 / 3xx redirects

    • Some platforms (e.g., Google Apps Script web apps) return 302 to a different URL.
    • LINE doesn’t follow redirects for webhooks; it treats a 302 as an error. Guides explicitly mention 302 from GAS causing webhook verification failures until a proxy is added. (Hugging Face Forums)

In all of these, LINE’s console may still show the same generic timeout-ish message even though the real cause is a specific status code.

3. Extra context for n8n and Hugging Face Spaces

You mentioned n8n and Hugging Face earlier, so I’ll connect the dots.

3.1 n8n-specific behavior

Relevant points from n8n community and docs: (n8n Community)

  • Webhook executions have a server-side timeout (about 1–2 minutes depending on setup). If your workflow takes longer, the HTTP client will see a timeout or no response.
  • Respond to Webhook sends the response only when it is reached in the workflow. If you put it after slow nodes or Wait nodes, the calling service waits the entire time.
  • Long-running workflows and large payloads can block the instance and delay other webhook executions.
  • When self-hosted or behind a proxy, the WEBHOOK_URL and host/port config must be correct. Otherwise, generated callback URLs sent to external services are wrong and cause 404/502.

For a LINE webhook:

  • If your n8n workflow does slow HTTP calls to HF Spaces before returning to LINE, LINE will almost always hit its 2-second limit first.
  • If any node throws (e.g., HTTP node gets 502 from a Space), n8n may respond with 500 or nothing, which LINE records as an error.

3.2 Hugging Face Spaces behavior

From Spaces-related posts: (Hugging Face Forums)

  • Spaces sleep when idle (depending on hardware / settings). Waking up and booting the app can take tens of seconds or more.
  • If the app never binds to the expected port within an internal timeout (e.g. 30 minutes), the platform marks it unhealthy and frontends return errors like 502.
  • Changes in infra, base images, or library versions can cause apps that used to work to suddenly fail during startup if they relied on fragile assumptions.

In your stack:

  • LINE → n8n (on Spaces) → maybe other Spaces/models
    If n8n’s container is cold or if a downstream Space is unhealthy and returns 502, the webhook request is delayed or fails and LINE reports a timeout.

4. Concrete solution patterns

Now the useful part: what to actually do.

4.1 First, confirm which bucket you are in

  1. Check LINE’s error statistics for your channel

    • It will show which reason is dominant: could_not_connect, request_timeout, or error_status_code. (LINE Developers)

  2. Hit your webhook URL from outside using curl or a simple HTTP client

    For example:

    curl -i -X POST "https://your-webhook-url.example.com/callback" \
  -H "Content-Type: application/json" \
  -d '{"ping": true}'

    Check:

    • HTTP status (must be 200–299).
    • Response time (should be well under a second if you’re just testing).
    • Any 30x/40x/50x means you’re in “error_status_code” territory.

  3. Look at your app / n8n logs for each webhook attempt

    • Do you see the request at all? If not, think could_not_connect.
    • Do you see it start but not finish quickly? Think request_timeout.
    • Do you see stack traces or 500s? Think error_status_code.

4.2 If the problem is “too slow” (request_timeout)

Goal: return 200 fast, push heavy work to the background.

Patterns:

  1. Early response flow

    In n8n or your framework:

    • Webhook node receives the request.

    • Immediately send 200 with Respond to Webhook (or equivalent).

    • In parallel, continue processing:

      • Call HF Spaces / models.
      • Make AI or DB calls.
      • Finally, use LINE’s reply or push API (using the replyToken or user ID from the event) to send messages.

    This is exactly how many GAS + LINE guides solve the timeout problem: a lightweight front (Cloud Function or Apps Script) responds instantly, then forwards to heavy logic. (Hugging Face Forums)

  2. Avoid long blocking waits

    • Do not put Wait nodes, complex branching, or long running loops before the Respond to Webhook.
    • n8n threads show issues when Wait nodes exceed 64 seconds or workflows run very long, causing webhook timeouts. (n8n Community)

  3. Use queues / secondary workflows

    • Use the webhook to enqueue work (DB, message queue, another HTTP endpoint).
    • Have a separate scheduled or triggered workflow pick up jobs and call external APIs without blocking LINE’s request.

  4. Mitigate cold starts

    • Use a simple uptime monitor or scheduler to ping your HF Space periodically (e.g., every few minutes).
    • This reduces cold boot frequency so LINE’s requests are more likely to hit a warm instance. HF threads show cold boot delays in the tens of seconds; keeping the Space warm helps. (Hugging Face Forums)

4.3 If the problem is “non-2xx response” (error_status_code)

Fix the actual HTTP failure:

  1. Make sure the route and method are correct

    • Match LINE’s configured path exactly (e.g., /callback vs /line/callback).
    • Accept POST; do not reject with 405.
    • Double-check with logs from your server or reverse proxy.

  2. Handle exceptions

    • Wrap webhook logic in try/catch so unexpected errors still produce a 200 response (or at least a controlled 4xx/5xx that you can treat as a bug, not as a crash).
    • For n8n, inspect the “Executions” tab for failed runs triggered by the webhook and fix whichever node is red (typically HTTP Request nodes or Function nodes).

  3. Do not rely on redirects

    • If your environment returns 302 (like some GAS deployments), put a proxy or front that returns 200 directly. LINE does not follow 3xx for webhook URLs. (Hugging Face Forums)

  4. Check upstream APIs (HF Spaces, inference endpoints)

    • If a Space is down, misconfigured, or still “Building/Starting,” it may respond with 502/503 or not at all. (Hugging Face Forums)

    • In your integration code, treat those as recoverable:

      • retry with backoff,
      • or short-circuit and still send a friendly error message to the user.

4.4 If the problem is “cannot connect” (could_not_connect)

  1. Verify URL syntax and DNS

    • Use a browser or curl from a machine outside your network to access the webhook URL.
    • Make sure it’s https://, no typos, and resolves to the expected host. (LINE Developers)

  2. TLS compatibility

    • Ensure your server’s TLS configuration meets LINE’s webhook TLS spec (cipher suites, protocols). (LINE Developers)

  3. Check proxies / tunnels / routers

    • If using ngrok or similar, confirm it is running and pointing to the correct local port. Real-world examples show the same error when tunnels return 502 / 404. (Learn Code With Mike)
    • Check firewalls, corporate proxies, or home routers that might block LINE’s IP ranges.

5. Short recap

  • The error text means: LINE’s platform did not get a valid 2xx response from your webhook quickly enough.

  • Under the hood, LINE classifies failures into:

    • could_not_connect (network / TLS / DNS),
    • request_timeout (server too slow, >~2s),
    • error_status_code (4xx/5xx/3xx). (LINE Developers)

  • In typical LINE bot setups (ngrok, Heroku, GAS, n8n, Hugging Face Spaces), common root causes are:

    • URL or path mismatch, wrong port, or tunnel not running. (Learn Code With Mike)
    • Slow or blocking logic inside the webhook (AI calls, DB, Sheets) and cold start delays. (Hugging Face Forums)
    • 3xx/4xx/5xx responses due to framework errors, app crashes, or upstream APIs failing. (Hugging Face Forums)

  • Robust pattern:

    • Make the webhook handler return 200 fast.
    • Move heavy work off the critical path (background workflows, queues, or secondary endpoints).
    • Keep your hosting environment healthy and warm, and handle upstream API errors explicitly.