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Common Issues

This guide covers common issues you may encounter when running the Price Tracker Bot and how to resolve them.

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Symptoms

  • Bot doesn’t reply to commands
  • No messages received from the bot
  • Bot appears offline in Telegram

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Possible Causes & Solutions

Missing TELEGRAM_TOKEN: If you see the error message ❌ TELEGRAM_TOKEN no definido en .env, your bot token is not configured.
Solution:
  1. Create a .env file in the project root
  2. Add your token: TELEGRAM_TOKEN=your_token_here
  3. Get your token from @BotFather on Telegram
  4. Restart the bot
The bot checks for this token at startup (index.mjs:12-14) and will exit if not found.
Polling Errors: Check your console for messages like ❌ Polling error:Common polling issues:
  • Network connectivity problems
  • Token revoked or invalid
  • Multiple instances of the bot running
Solution:
  1. Verify your token is correct
  2. Check your internet connection
  3. Stop all other instances: pkill -f "node.*index.mjs"
  4. Restart the bot
The bot logs polling errors at index.mjs:715.

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Symptoms

  • Error: ❌ No se pudo obtener información del producto
  • Products fail to add
  • Price checks return errors

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Playwright Not Installed

If you see browser launch errors, Playwright browsers may not be installed.
Solution:
npx playwright install chromium
The bot uses Playwright’s Chromium browser for scraping (index.mjs:6, 148).

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Amazon Blocking Requests

Symptoms:
  • Error: Título no encontrado (index.mjs:127)
  • Error: Precio inválido o no encontrado (index.mjs:129)
Possible causes:
  • Amazon detected automated scraping
  • Product page structure changed
  • Geographic restrictions
  • Rate limiting
Solutions:
The bot includes delays between requests (800-900ms at index.mjs:78, 214) to avoid rate limiting.
  1. Wait and retry: Amazon may temporarily block requests
  2. Check URL: Ensure the URL is a valid Amazon product page
  3. Try different products: Test with multiple products to isolate the issue
  4. Review selectors: Amazon may have changed their HTML structure
The scraper tries multiple CSS selectors for title (index.mjs:81-93), price (index.mjs:96-109), and images (index.mjs:112-125).

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Invalid Product URL

Error messages:
  • ❌ URL inválida. Debe iniciar con http(s). (index.mjs:401)
Solution: Ensure your URL:
  • Starts with http:// or https://
  • Points to an Amazon product page
  • Contains product identifier (/dp/ or /gp/)
Example valid URL:
https://www.amazon.com/dp/B08N5WRWNW

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Symptoms

  • Prices never change
  • No automatic checks happening
  • /check command times out

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Cron Jobs Not Running

The bot has two scheduled tasks:
  • Price checks: Every 2 hours (index.mjs:733)
  • Daily summary: Every day at 20:00 (index.mjs:720)
Verify cron is working:
  • Check console for: 🔄 Cron: revisión automática de precios...
  • Look for: ⏳ Iniciando revisión de precios...
Common issues:
  • Bot process stopped or crashed
  • System time incorrect
  • No products added to track
Solution:
  1. Keep the bot running continuously
  2. Use a process manager like pm2: 
    npm install -g pm2
pm2 start index.mjs --name price-tracker
pm2 save
  3. Check system time: date

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Errors During Price Checks

Console messages to look for:
  • ❌ Error en cron checkPrices: (index.mjs:738)
  • ⚠️ Errores durante la revisión: (index.mjs:249)
The bot continues checking other products even if one fails (index.mjs:165-172).Debug steps:
  1. Run manual check: /check command
  2. Watch console output for specific errors
  3. Test individual product URLs
  4. Review error logs for patterns

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No Products Being Tracked

If you see: ℹ️ No hay productos para revisar. (index.mjs:142)Solution:
  • Add products using /add [URL]
  • Verify products saved: /list
  • Check prices.json file exists and contains data

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Symptoms

  • Products disappear after restart
  • Price history missing
  • Chat registrations lost

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File Permission Problems

Error: ❌ Error guardando datos: (index.mjs:46) indicates file write failures.
Check permissions:
ls -la prices.json
Fix permissions:
chmod 644 prices.json
The bot saves data to prices.json after every change (index.mjs:20, 41-48).

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JSON Corruption

Error: ❌ Error al cargar datos: (index.mjs:32)This happens when prices.json contains invalid JSON.Solution:
  1. Backup the file: cp prices.json prices.json.backup
  2. Validate JSON: 
    cat prices.json | python -m json.tool
  3. Fix syntax errors or restore from backup
  4. If unrecoverable, delete and start fresh: 
    rm prices.json

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Disk Space Issues

Check available space:
df -h .
The bot stores:
  • Product data in prices.json
  • Up to 120 price history entries per product (HISTORY_LIMIT at index.mjs:69)
History is automatically limited to the last 120 entries per product (index.mjs:196).

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Data File Not Created

If you see: ℹ️ No existe prices.json — se creará al guardar. (index.mjs:37)This is normal on first run. The file is created automatically when you add your first product.Verify file creation:
  1. Add a product: /add [URL]
  2. Check file exists: ls -la prices.json
  3. Review contents: cat prices.json

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Symptoms

  • Bot crashes during price checks
  • High memory usage
  • Timeouts on /check or /add

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Browser Launch Failures

The bot launches Chromium with specific args (index.mjs:148, 412):
{ headless: true, args: ["--no-sandbox", "--disable-dev-shm-usage"] }
Solutions:
The --no-sandbox flag is necessary when running as root or in containers.
  1. Install browser dependencies (Linux): 
    sudo apt-get install -y \
  libnss3 libnspr4 libatk1.0-0 libatk-bridge2.0-0 \
  libcups2 libdrm2 libxkbcommon0 libxcomposite1 \
  libxdamage1 libxrandr2 libgbm1 libpango-1.0-0 \
  libcairo2 libasound2
  2. Increase shared memory (Docker): 
    docker run --shm-size=2gb ...

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Timeout Errors

Default timeout: 60 seconds (index.mjs:75)If pages load slowly:
  1. Check internet speed
  2. Try different Amazon region
  3. Test with simpler products (fewer images/reviews)

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Memory Leaks

The bot properly closes browsers after each operation:
  • Price checks: index.mjs:217
  • Add product: index.mjs:417
  • Edit product: index.mjs:566
  • Chart generation: index.mjs:305
Monitor memory:
ps aux | grep node
If memory grows continuously:
  1. Restart the bot daily using cron
  2. Reduce check frequency
  3. Limit number of tracked products

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Symptoms

  • No price drop alerts received
  • Some chats not receiving notifications
  • Error sending messages

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Chat Not Registered

The bot auto-registers chats on first message (index.mjs:705-712).Verify registration:
  1. Send /start to the bot
  2. Check console for: 🎉 Nuevo chat registrado: [chatId]

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Message Send Failures

Error: ❌ Error enviando notificación a [chatId]: (index.mjs:239)Causes:
  • User blocked the bot
  • Chat no longer exists
  • Bot doesn’t have permission
The bot continues notifying other chats even if one fails (index.mjs:223-244).

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No Price Drops Detected

The bot only notifies when price decreases (index.mjs:199-207).Check logic:
  • Compares scraped.price < originalPrice
  • Calculates difference and percentage
  • Shows historical lowest price
If prices clearly dropped but no alert:
  1. Check console: ℹ️ No se detectaron bajadas de precio
  2. Verify price data in prices.json
  3. Run /check manually to test
  4. Review console for comparison values

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Getting Help

If you’re still experiencing issues:
  1. Check console logs for error messages
  2. Review prices.json for data integrity
  3. Test with a fresh product to isolate the problem
  4. Open an issue on GitHub with:
    • Error messages from console
    • Steps to reproduce
    • Your environment (OS, Node version)
    • Relevant section of prices.json (redact URLs if sensitive)
Most errors are logged with ❌ prefix in the console. Always check logs first when troubleshooting.

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