https://devzone.nordicsemi.com/f/nordic-q-a/44059/use-of-nus_data_send-in-user-made-data-send-functionHi everyone, I want to transmit a HEX array I read from a peripheral using SPI communication (I initialize my RX_BUF in the SPI_EVT_HANDLER() function) via BLE. I am using a mobile app (nrfConnect and nrf Toolbox) to receive data from the device. Theen-USTelligent Community 13Mon, 25 Feb 2019 15:15:44 GMThttps://devzone.nordicsemi.com/thread/172833?ContentTypeID=1Mon, 25 Feb 2019 15:15:44 GMT137ad170-7792-4731-bb38-c0d22fbe4515:0e1d8ee8-5d76-4fd1-8e83-7d4c2038b88eHung Bui<p>Hi,&nbsp;</p> <p>When you see something doesn&#39;t work as expected. Please try to debug.&nbsp;</p> <p>To debug in this case you would need to check the return code of the API(s) you call,&nbsp;ble_nus_data_send() . YOu need to check if it return err_code = NRF_SUCCESS or not.&nbsp;</p> <p>You can also step into the code and see which exact function return the error code if it&#39;s not normal (NRF_SUCCESS). Most likely the error comes from&nbsp;sd_ble_gatts_hvx() and then you can have a look at the description of the function and have a suggestion on why that happened.</p> <p>I would suspect that it was because the connection has not been established and the CCCD (notification) was not enabled.&nbsp;</p><div style="clear:both;"></div>