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docs/TROUBLESHOOTING.md

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+# 🔧 Troubleshooting Guide for 404 and 502 Errors
+
+## Quick Diagnosis
+
+Run these commands on your Ubuntu server to diagnose the issue:
+
+```bash
+# 1. Check if files exist
+ls -la /var/www/dexarmarket/browser/index.html
+
+# 2. Check nginx config syntax
+sudo nginx -t
+
+# 3. Check nginx error logs (THIS IS MOST IMPORTANT!)
+sudo tail -30 /var/log/nginx/error.log
+
+# 4. Check if nginx is running
+sudo systemctl status nginx
+
+# 5. Test API from server
+curl -v https://api.dexarmarket.ru:445/ping
+```
+
+## Error: 404 Not Found
+
+### Cause: Files not uploaded or wrong path
+
+**Solution 1: Verify files are on server**
+```bash
+ls -la /var/www/dexarmarket/browser/
+```
+
+Should show:
+- `index.html`
+- `main-*.js`
+- `chunk-*.js`
+- `polyfills-*.js`
+- `styles-*.css`
+- `assets/` folder
+
+**If files are missing:**
+```bash
+# From your local machine:
+cd F:\dx\marketplace\Dexarmarket
+npm run build
+scp -r dist/dexarmarket/browser/* user@your-server:/var/www/dexarmarket/browser/
+```
+
+**Solution 2: Fix permissions**
+```bash
+sudo chown -R www-data:www-data /var/www/dexarmarket
+sudo chmod -R 755 /var/www/dexarmarket
+```
+
+**Solution 3: Check nginx config is loaded**
+```bash
+# Check which config is active
+ls -la /etc/nginx/sites-enabled/
+
+# Should show symlink to dexarmarket config
+# If not:
+sudo ln -s /etc/nginx/sites-available/dexarmarket /etc/nginx/sites-enabled/
+sudo nginx -t
+sudo systemctl reload nginx
+```
+
+**Solution 4: Verify nginx root path**
+```bash
+sudo cat /etc/nginx/sites-available/dexarmarket | grep root
+```
+
+Should show: `root /var/www/dexarmarket/browser;`
+
+## Error: 502 Bad Gateway
+
+### This means the API backend (https://api.dexarmarket.ru:445) is unreachable
+
+**Solution 1: Check if API is running**
+```bash
+# From Ubuntu server:
+curl -v https://api.dexarmarket.ru:445/ping
+
+# If this fails, your API backend is down!
+```
+
+**Solution 2: Port 445 is blocked**
+Port 445 is typically blocked by many firewalls because it's used for SMB file sharing.
+
+**Check from browser console (F12):**
+- Open browser Developer Tools (F12)
+- Go to Console tab
+- Look for errors like: `net::ERR_CONNECTION_REFUSED` or `net::ERR_SSL_PROTOCOL_ERROR`
+
+**Possible fixes:**
+- Use standard port 443 for HTTPS
+- Or use port 8443, 8080, or other non-standard but common ports
+- Configure firewall to allow port 445
+
+**Solution 3: CORS issues**
+The API must have CORS headers allowing requests from `https://dexarmarket.ru`
+
+Check API response headers:
+```bash
+curl -v -H "Origin: https://dexarmarket.ru" https://api.dexarmarket.ru:445/ping
+```
+
+Should include headers like:
+```
+Access-Control-Allow-Origin: https://dexarmarket.ru
+```
+
+**Solution 4: SSL Certificate issues**
+```bash
+# Test with SSL verification disabled
+curl -k https://api.dexarmarket.ru:445/ping
+
+# If this works but normal curl doesn't, SSL cert is invalid
+```
+
+## Still Not Working?
+
+### Get detailed error information:
+
+**1. Browser Console (JavaScript errors)**
+```
+F12 → Console tab
+Look for red errors
+```
+
+**2. Browser Network Tab (Failed requests)**
+```
+F12 → Network tab
+Reload page
+Look for red (failed) requests
+Click on failed request to see details
+```
+
+**3. Nginx Error Log (Server-side errors)**
+```bash
+sudo tail -50 /var/log/nginx/error.log
+```
+
+**4. Nginx Access Log (See what requests come in)**
+```bash
+sudo tail -50 /var/log/nginx/access.log
+```
+
+**5. Test Build Locally**
+```bash
+cd F:\dx\marketplace\Dexarmarket\dist\dexarmarket\browser
+python -m http.server 8000
+# Visit http://localhost:8000
+```
+
+If local test works, the issue is with deployment, not the build.
+
+## Common Mistakes
+
+❌ **Uploading to wrong directory**
+- Correct: `/var/www/dexarmarket/browser/`
+- Wrong: `/var/www/dexarmarket/` (missing browser/)
+
+❌ **Wrong permissions**
+```bash
+# Must be readable by www-data
+sudo chown -R www-data:www-data /var/www/dexarmarket
+sudo chmod -R 755 /var/www/dexarmarket
+```
+
+❌ **Nginx config not reloaded**
+```bash
+# After ANY change to nginx config:
+sudo nginx -t
+sudo systemctl reload nginx
+```
+
+❌ **Old files cached**
+```bash
+# Clear browser cache: Ctrl+Shift+R (hard refresh)
+```
+
+❌ **API port blocked**
+- Port 445 is unusual and often blocked
+- Consider using port 443 (standard HTTPS)
+
+## Contact Information for Support
+
+When asking for help, provide:
+1. Output of `sudo nginx -t`
+2. Last 30 lines of nginx error log: `sudo tail -30 /var/log/nginx/error.log`
+3. Browser console errors (F12 → Console)
+4. Result of `curl -v https://api.dexarmarket.ru:445/ping` from server
+5. Screenshot of browser Network tab showing failed request