Hi,
I am sorry that there is not enough documentation regarding this option. I will try to explain it here.
The way 'Retry of fail' option works in 'Data to Server' is that if the server is unreachable, then it will collect source data (for example, Modbus data) and will try to send it on the next retry, depending on the configured interval. If the second try fails, it will continue to store data and will try again until it will be able to reach the server.
Now, this refers to the TCP/IP connection and not the HTTP response code. It does not matter if the server returns 200,400, or 404. The router was able to connect to the server, so it considers it a success and will not store the data. If the server is down or the link is down, then the server is unreachable and the device will start storing data.
Kind Regards,
Andzej