You're reading the documentation for an older, but still supported version (GL013300).
For information on the latest version, please have a look at GL013301.

7.1 Connection Refused (API Link Error)

This issue occurs when the API fails to establish a connection with the robot controller or emulator.

A. Error Case

During initialization, the following error message may appear:

[Error] Connection refused by host
[Info] Failed to connect to 192.168.137.100:12345

B. Root Cause Analysis

This error typically indicates one of the following:

The DART Platform or Emulator is not running. (in virtual mode)
The target IP address or port is incorrect.
A firewall or VPN is blocking the connection.

C. Solution

Start the DART Platform or Emulator before running your API program.
Verify the robot IP configuration in your code:
```
Drfl.open_connection("192.168.137.100");
```

Confirm network access with ping or netcat:

ping 192.168.137.100
nc -zv 192.168.137.100 12345

If running on a company network, check internal firewall settings.
Disable any active VPNs that may interfere with local network connections.
Ensure no other applications are using the same port (12345/TCP).
Restart your PC and robot controller/emulator to clear any stale network states.