How to use validator properly (python)

gvimvim 8.1 1-26/windows10

flake8 installed via: pip install flake8

vimrc:

let g:validator_highlight_message = 1
let g:validator_auto_open_quickfix = 1
let g:validator_error_msg_format = "[ ● %d/%d issues ]"
let g:validator_debug = 1

When I tried to issue :ValidatorCheck against python file buffer, vim echo this error message:
E119: Not enough arguments for function <SN>58_check

I tried to make some errors and use flake8 directly from cmd, this is what I got:

__init__.py:65:1: E305 expected 2 blank lines after class or function definition, found 1
__init__.py:65:1: F821 undefined name 'classd'
__init__.py:66:1: E302 expected 2 blank lines, found 0

some color changes:

  hi ValidatorErrorSign guifg=#F98365
  hi ValidatorWarningSign guifg=#546E7A

:copen gives empty output.
validator.log is empty