An unmanned aerial vehicle (UAV) is disclosed that includes a retractable payload delivery system. The payload delivery system can lower a payload to the ground using a delivery device that secures the payload during descent and releases the payload upon reaching the ground. The delivery device can include a channel in which a payload mount attachment for a payload can be inserted. The payload mount attachment can include an aperture for receiving a retaining rod to secure the attachment, and thus the payload, to the delivery device. The retaining rod can assume either an engaged position, in which a portion of the retaining rod engages the payload mount attachment while the payload mount attachment is inserted in the channel, or a disengaged position, in which the retaining rod does not engage the payload mount attachment.