Do you have a bit more information? How did you send it, what does your project look like? Did you try to capture a sniffer trace of the network, using the nRF sniffer for 802.15.4? Can you see the packet over the air? If not, did the function call you used to send the message return anything? If so, did the return value indicate that it was sent successfully, or did it return a value indicating an error?
