Sending commands to API port

I've connected the USB Embedded Network Manager (DC2274A-A) to my labtop. I've written a program that reads and sends byte arrays from the serial port. I've successfully received the MgrHello packet and responded with the Hello packet. I've then received the HelloResponse packet. Now I'm trying to send a command. According to the API port Guide: (page 19) The command should be formatted as Serial API Header | Request structure. The serial API Header is Control, Packet Type, Sequence Number, and Payload Length. I'm trying to send the command getNetworkInfo (0x40). Command is 0x02, Packet Type is: 0x40, Sequence Number is 0x01 (I received 0x00 from HelloResponse), Payload Length is 0x00 since there is no request structure. So i'm sending 0x02 0x40 0x01 0x00 to the serial port and i'm getting nothing. What am I doing wrong?