Hi Hugo,
The 3 minutes and 50 seconds probably is due to the firewall cancelling the request because it is open for too long. Azure WAF for instance typically do this after 240 seconds.
You can indeed use the start_commit for this, as it queues the import as a task on the background.
To figure out if the import is done, you can periodically call the “end_commit” endpoint. It will return status code 202 when it is still busy.
When it is done, a Http 200 is returned and in the response you can find out how many rows are imported, failed or the url to download the errors.
Regards,
Dick van den Brink