Downgrading from android 7.1.2 to 7.1.1

[AC Question]

While downgrading using mac for my pixel, faced the following error.

Paruls-MacBook-Pro:sailfish-nmf26o parularora$ fastboot --slot other --skip-secondary update image-sailfish-nmf26o.zip
ERROR: could not get pipe properties for endpoint 1 (e0004061)
target reported max download size of 536870912 bytes
archive does not contain 'boot.sig'
archive does not contain 'recovery.img'
archive does not contain 'system.sig'
archive does not contain 'vendor.sig'
--------------------------------------------
Bootloader Version...: 8996-012001-1704121145
Baseband Version.....: 8996-012901-1702171013
Serial Number........: FA6AA0301566
--------------------------------------------
checking product...
OKAY [ 0.050s]
checking version-bootloader...
FAILED

Device version-bootloader is '8996-012001-1704121145'.
Update requires '8996-012001-1610061102'.

finished. total time: 0.300s

Please Help