Troubleshoot

grammY — Troubleshooting

Symptoms first, root causes next. Grouped by the layer where the bug actually lives — your token, Telegram, your code, your TypeScript, your deploy.

401 Unauthorized

Cause: bot token is wrong, missing, or revoked.

Fix:

echo $BOT_TOKEN          # confirm the env var is set
curl "https://api.telegram.org/bot$BOT_TOKEN/getMe"
# Should return {"ok":true,"result":{"id":...,"username":"..."}}

If getMe fails too, regenerate the token via /token in BotFather.

409 Conflict: terminated by other getUpdates request

Cause: two processes are simultaneously fetching updates for the same bot.

Common scenarios:

• Local npm run dev + deployed bot both polling.
• Deployed with both bot.start() AND webhookCallback() registered.
• A previous deploy is still running on the host.

Fix: stop the duplicate process. To verify nothing else is polling:

curl "https://api.telegram.org/bot$BOT_TOKEN/getWebhookInfo"

If url is non-empty you have a webhook set — bot.start() will fight it. Either delete the webhook (deleteWebhook) or remove bot.start().

429 Too Many Requests: retry after N

Cause: hit Telegram's rate limits.

Fix: install both rate-limit plugins (see scaling-runner):

bot.api.config.use(apiThrottler());
bot.api.config.use(autoRetry({ maxAttempts: 3, maxDelaySeconds: 10 }));

Bot replies twice to every message

Cause: long polling + webhook both active in the same process.

Fix: pick one. If using webhooks, remove bot.start(). If using polling, call bot.api.deleteWebhook({ drop_pending_updates: true }) on startup.

Bot doesn't respond at all

Checklist in order:

1. curl …/getMe → token works.
2. curl …/getWebhookInfo → either webhook URL is correct or url is empty (then you must be polling).
3. Process log shows [grammY] You can stop me by pressing Ctrl+C (polling) or your HTTP server log shows incoming requests (webhook).
4. bot.start() or webhookCallback() is actually called (check for missing await or unreachable code).
5. Filter query matches what you're sending (bot.on("message:text", …) doesn't match a photo).
6. No middleware before the handler is returning without next().

TypeScript: Property 'session' does not exist on type 'Context'

Cause: you installed session() but didn't add SessionFlavor to your context type.

Fix:

type MyContext = Context & SessionFlavor<MyData>;
const bot = new Bot<MyContext>(token);

Same applies to every plugin that augments context: ConversationFlavor, HydrateFlavor, ParseModeFlavor, ChatMembersFlavor, etc. Combine them:

type MyContext = HydrateFlavor<ConversationFlavor<Context & SessionFlavor<MyData>>>;

conversation.wait never resolves

Checklist:

1. Did you mount the session plugin before conversations()? Without session, conversation state isn't persisted.
2. Did you call bot.use(createConversation(myConvo, "name")) AND ctx.conversation.enter("name")?
3. Inside the conversation, do you call await conversation.wait*() — never plain await new Promise(...)?
4. Inside the conversation, do you wrap non-deterministic calls (fetch, randomUUID, Date.now) in conversation.external(() => …)?

"Cannot serialize conversation"

You stored something non-serializable in conversation.session (a function, class instance, Map, Set). Conversations must only hold JSON-compatible values. Wrap non-serializable computation in conversation.external.

ctx.reply works but ctx.api.sendMessage(otherChatId, …) fails with "chat not found"

Cause: your bot has never met that chat, OR you used a username instead of an id.

Fix:

• For private chats: the user must /start your bot at least once.
• For groups/channels: your bot must be a member (and admin for channels).
• Use chat id (number), not @username, except for public channels.

Webhook errors

getWebhookInfo returns last_error_date / last_error_message. Common ones:

Message is too long

Telegram caps text at 4096 chars. Split before sending:

function chunk(text: string, size = 4000): string[] {
  const out: string[] = [];
  for (let i = 0; i < text.length; i += size) out.push(text.slice(i, i + size));
  return out;
}
for (const part of chunk(longText)) await ctx.reply(part);

Markdown / HTML formatting errors

Bad Request: can't parse entities means your text breaks the chosen parse_mode.

• For MarkdownV2: every literal _ * [ ] ( ) ~ ` > # + - = | { } . ! must be escaped with \\ (in TS source).
• Easier: install @grammyjs/parse-mode and use the bold(text), italic(text) builders which escape for you.

"Cannot find module 'grammy'" or similar import failure

npm ls grammy           # is it installed?
node -e "console.log(require.resolve('grammy'))"

If using ESM with "type": "module", import as import { Bot } from "grammy" (no .js). If using TypeScript with "moduleResolution": "node16", you may need .js suffixes on relative imports — see your tsconfig.

Long polling stops after one update

Cause: handler threw synchronously and you didn't install bot.catch. The polling loop crashes.

Fix: install bot.catch (see error-handling).

Deno: "Uncaught (in promise) Forbidden: bot was blocked by the user"

Same as everywhere — the user blocked your bot, but the error reached top-level. Install bot.catch and ignore or log this case.

When all else fails

1. Enable debug logs: DEBUG=grammy* node ./src/bot.js.
2. Inspect raw updates: bot.use((ctx) => { console.log(JSON.stringify(ctx.update, null, 2)); }).
3. Check getWebhookInfo (webhook) or getMe (polling).
4. Search https://github.com/grammyjs/grammY/issues for the exact error.
5. Open https://t.me/grammyjs — the official chat.