The wireless power transmitter 100 in the power transfer state 640 transmits power to the wireless power receiver 200.
The wireless power transmitter 100 may receive a power control message from the wireless power receiver 200 while transferring power, and control a characteristic of the power applied to the transmitting coil in response to the received power control message. For example, the power control message used to control a characteristic of the power applied to the transmitting coil may be included in a control error packet 5500 as illustrated in 
The wireless power transmitter 100 may monitor parameters within a power transfer contract generated based on the identification information and/or configuration information in the power transfer state 640. As a result of monitoring the parameters, if power transmission to the wireless power receiver 200 violates the limits included in the power transfer contract, then the wireless power transmitter 100 may cancel the power transmission and return to the selection state 610.