I able to unlock a Z520a with HWK as an experiment and it was successful, as follows:
1. Connect phone then 'go' to boot, u can see if it RED or BROWN.
(since your phone is RED, you can try what I did because mine was RED, also Im working on another one which is BROWN but post result later if success)
2. Click 'flash Mcu' to flash MCU only (with Z520 flash files from
www.ufsxhwk.com)
3. Click 'Init Sb' to unlock.
(check at this stage, insert sim and test otherwise continue to 4.)
4. Click 'Restore'
(when completed, insert and try). If failed, redo all from 1. to 4. If failed, say a prayer.
Note: Experts may know better, but my little experiment or playing I did able to unlock my Z520a phones (RED). Im working on BROWNs and see what gonna happen.
cheers.