https://devzone.nordicsemi.com/f/nordic-q-a/41282/write-data-to-control-point-characteristic-failedHello, I&#39;m using a nrf51822 board as a DFU controller to update another board&#39;s application, the client board runs the bootloader secure example. When I write data to the control point characteristic, the client board does not generate any event. Iten-USTelligent Community 13Fri, 07 Dec 2018 00:28:23 GMThttps://devzone.nordicsemi.com/thread/160648?ContentTypeID=1Fri, 07 Dec 2018 00:28:23 GMT137ad170-7792-4731-bb38-c0d22fbe4515:1d65a63c-fccd-44ef-bf23-292f711fecdaNothing<p>Hi,</p> <p>Thanks for your answer. I&#39;m sending data from the server to the client. And I have found the problem, the write_op should be&nbsp;BLE_GATTS_OP_WRITE_REQ.&nbsp; But what&#39;s the differences between&nbsp;<span>BLE_GATTS_OP_WRITE_REQ and&nbsp;BLE_GATTS_OP_WRITE_CMD.</span></p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/160583?ContentTypeID=1Thu, 06 Dec 2018 13:26:18 GMT137ad170-7792-4731-bb38-c0d22fbe4515:34b1a2e8-6e10-4519-ac86-df52e16be1ddSigurd<p>Hi,</p> <p>So you are sending a write command from the client to the server? If the characteristic requires authorization(<span>wr_auth set to true when configuring the&nbsp;characteristic</span>),you will on the server receive a BLE_GATTS_EVT_WRUTE event with auth_required flag set to 1. Then you need to call sd_ble_gatts_value_set on the server. See <a href="https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s130.api.v2.0.1/group___b_l_e___g_a_t_t_s___w_r_i_t_e___c_m_d___a_u_t_h___m_s_c.html?cp=3_7_2_1_0_2_4_3_17">this message sequence chart</a>.</p><div style="clear:both;"></div>