PCA10056 can not upgrade with UART

PCA10056 can not upgrade with UARThttps://devzone.nordicsemi.com/f/nordic-q-a/57745/pca10056-can-not-upgrade-with-uartHi, I use example nRF5SDKforThreadandZigbeev3209fade31\examples\dfu\secure_bootloader\pca10056_uart to upgrade bootloader and coordinator application. I try to upgarde PCA10056 with 'nrfutil -v -v -v -v dfu serial -pkg boot_uart_ok_arm_0F.zip -p COM20en-USTelligent Community 13Thu, 13 Feb 2020 14:13:08 GMTRE: PCA10056 can not upgrade with UARThttps://devzone.nordicsemi.com/thread/234206?ContentTypeID=1Thu, 13 Feb 2020 14:13:08 GMT137ad170-7792-4731-bb38-c0d22fbe4515:cde8615f-2a63-479b-acc6-63b71563262bHung Bui<p>Hi, </p> <p>Could you give the log when it not successful ? (and also when it's successful) </p> <p>What do you have on COM20 ? <br />Are you connecting 2 PCA10056 to the PC ? <br /> </p><div style="clear:both;"></div>