Sending this json with a binary header to the down port of the packet forwarder should also work. The PROTOCOL.TXT file referenced above provides the info needed for the header.
{"txpk":{"codr":"4/5","data":"oFxUlwEQRAAB8UObZx4=","datr":"SF8BW125",,"freq":921.9,"ipol":false,"modu":"LORA","ncrc":true,"powe":20,"rfch":0,"size":14,"imme":true}}
Try to install the usb gateway utils.
opkg update
opkg install lora-gateway-usb-utils
This will create directory /opt/lora
If opkg cannot connect to feed you can update the url in the following file
Check /etc/opkgd/mlinux-feed.conf
To find the mlinux version
cat /etc/issue
A list of feed paths are available here
http://multitech.net/mlinux/feeds/