How to pass `Chk` parameter to dotpay payments gateway in Django (Saleor)

Question

I'm having having difficulties integrating dotpay payment gateway in saleor. I'm not sure how am I suppose to pass Chk parameter to dotpay.

Saleor is using django-payments for that: https://github.com/mirumee/django-payments/blob/master/payments/dotpay/forms.py

Dotpay docs: https://ssl.dotpay.pl/s2/login/cloudfs1/magellan_media/common_file/dotpay_technical_manual_for_payments_implementation.pdf

So far I've got set up:

PAYMENT_VARIANTS = { 'dotpay': ('payments.dotpay.DotpayProvider', { 'seller_id': '123', 'pin': '0000', 'lock': True, 'endpoint': 'https://ssl.dotpay.pl/test_payment/'})} and

CHECKOUT_PAYMENT_CHOICES = [ ('default', 'Dotpay')]