python-redsys Redirect the user-agent with post method

Question

i use python-redsys : https://pypi.org/project/python-redsys/

I'm stuck at the step 4. Communication step

This is my view :

@login_required
def redsys_start(request):

    secret_key = DS_SECRET_KEY
    client = RedirectClient(secret_key)

    parameters = {
    "merchant_code": DS_MERCHANT_MERCHANTCODE,
    "terminal": DS_MERCHANT_TERMINAL,
    "transaction_type": STANDARD_PAYMENT,
    "currency": EUR,
    "order": "000000001",
    "amount": D("10.56489").quantize(D(".01"), ROUND_HALF_UP),
    "merchant_data": "test merchant data",
    "merchant_name": "Example Commerce",
    "titular": "Example Ltd.",
    "product_description": "Products of Example Commerce",
    "merchant_url": reverse('front:shop_cart_payment_callback'),
    }

    args = client.prepare_request(parameters)
    print(f"args =  {args}")
    context = {'args': args, 'BANK_PAIEMENT_URL': BANK_PAIEMENT_URL}

    # STEP 3
    args = client.prepare_request(parameters)

What i have to do after that fo redirect my customer to the red sys payement system ?

• If i try to redirect it with parameters redsys refuse because it is with get method
• If i try to make a form with args redsys give me an error SIS0431 (json Ds_MerchantParameters issue)

That is wahat the doc say :

4. Communication step

Redirect the user-agent to the corresponding Redsys' endpoint using the post parameters given in the previous step.

After the payment process is finished, Redsys will respond making a request to the merchant_url defined in step 2.

5. Create and check the response

Create the response object using the received parameters from Redsys. The method create_response() throws a ValueError in case the received signature is not equal to the calculated one using the given merchant_parameters. This normally means that the response is not coming from Redsys or that it has been compromised.

EDIT As requested my args variable content :

args = {'Ds_SignatureVersion': 'HMAC_SHA256_V1', 'Ds_MerchantParameters': b'SOMETHING', 'Ds_Signature': b'SOMETHING'}