xiaomi redmi 6 pro bootloader error

Device : Xiaomi Redmi 6 Pro
Operation : Bootloader Unlock/Relock
Checking for existing devices...Not Found
Turn Off phone, hold Vol UP + Vol DOWN and insert USB cable.
Some phones may need Special Boot Cable or TestPoint for EDL mode.
Found Port : Qualcomm HS-USB QDLoader 9008 (COM422)
Driver Info : Qualcomm Incorporated, qcusbser.sys, 2.1.2.2
Connecting to phone...OK
Waiting for response...OK
Init Handshake Sequence...OK
Hardware ID : E1600400 [8953] 00000000
OPK_DATA : 079E496E26A477B120DFCD85DF7E4AD067164D8292DDD37993 0D5891E3D8240B
Initializing Protocol...OK
Preparing Loader...Done
Sending Loader [Mi6Pro]...Write Error!
Please use correct loader and check USB port / cable.
Operation Finished.
QcFire Ver. 3.9