Possible causes:

• Server IP address not whitelisted in TapTopUp
• API key invalid or expired
• TapTopUp API temporarily unavailable
• Network connectivity issues

To fix:

• Check your server's public IP address (not your browser IP)
• Add the server IP to TapTopUp IP whitelist
• Wait a few minutes for IP whitelist to propagate
• Verify TAPTOPUP_API_KEY is correct in your environment variables