One of the things that can help us make progress is by looking into the logs. As you make this API call, can you share the fdk.log file that is generated? — Especially those log lines that indicate this API call is being made.
See how fdk.log helps in troubleshooting
Copy specific section of logs using Debug Mode
Share browser logs if you think those can help.
Also, do you mind sharing you iparams.json ?