Flush command is used to send records stored in device memory to the server different from that in device configuration.
When device is not able to send records to configured server it stores them in internal memory. When server is able to receive records all saved records will be sent, and when they are succesfully sent, they will be erased from internal memory.
From device anser "FLASH accepted: 0 records found on FLASH" you can see that there is no records saved in internal memory.
If you want to change your targer AVL server settings, please change Server Settings in device configuration using setparam command.
If you need more help with server configuration please provide your device type.