Your credit balance is empty

[Jane1]

I would like to flash Xiaomi Redmi Note 6 Pro . Here is the log

Scanning for Qualcomm HS-USB QDLoader 9008 device...
Download Port: Qualcomm HS-USB QDLoader 9008 (COM8)
Connection status: XHCI:HUB3:USB 2.00 High-Speed
USB Driver: [Qualcomm Incorporated] qcusbser, version: 2.1.2.7, date: 8-2-2017
Initializing...
MSM Serial number: 0x90ec86d1
MSM HW ID: 0x000cc0e1 (SDM636)
OEM Public Key Hash: 0xa7b8b82545a98eca23d6e9105fb464568d1b5828264903441bdef0cd57e3c370
SBL SW version: 4
Firehose: prog_emmc_firehose_Sdm660_ddr.elf
hash: 5debe372908b5ea112eee91a823aab4ad90f3c48, size: 653.64 KiB
QC_IMAGE_VERSION: BOOT.XF.1.4-00252-S660LZB-1
IMAGE_VARIANT: Sdm660LA
OEM_IMAGE_VERSION: c3-bsp-builder-job007.bj
Sending firehose loader... Done.
Handshaking...
Sending ping... Done.
Binary build date: Jan 2 2019 17:26:25
Chip serial num: 2431420113 (0x90ec86d1)
Sending configurations...
ERROR: Only nop and sig tag can be recevied before authentication.
Error: Your credit balance is empty, please TOP-UP first.
Authentication aborted.

Doeas it mean bootloader is locked and must me unlocked first?
How many credits are needed ?
Is there any pricelist?