I am on a high school robotics team, and we desperately want our robots to communicate with each other, but we are having some difficulties. Each robot has an XBee S2 connected to a Teensy 3.2 (essentially an arduino). We worked with the XBee library written by Andrewrapp. We are using the XBees in API mode. We got them so they successfully communicating; however, we want both the sending and receiving XBee to know when the communication between the XBees is successful. When the robots were within range of each other the sender received a successful status response, meaning the sender knew that the receiver successfully received the message. However, when we deliberately weakened the XBee communication by moving the XBees out of range from each other, the receiving robot successfully received a message from the sending robot, but the robot transmitting the message did not get a response that the message was successfully transmited. Is there a way that both XBees can know with 100% certainty whether the communication went through?