I was able to go through (https://www.odoo.com/forum/help-1/question/register-payment-using-xmlrpc-44048) and make a sales voucher after activating the voucher module. However, workflow('account.voucher', 'proforma_voucher', voucher_id) just does not work.

How can I achieve this? So far, what I have noted I can create a draft payment as follows:

    # Fetch the invoice    invoice = self.execute_kw('account.invoice', 'search_read', [[        ['number', '=', billRefNumber]    ]])[0]
    # Fetch the payment method    payment_method = self.execute_kw('account.payment.method', 'search_read', [[        ['payment_type', '=', 'inbound'],        ['code', '=', 'manual']    ]])[0]
    # Get the journal index    journal = self.execute_kw('account.journal', 'search_read', [[        ['code', '=', 'CSH1']    ]])[0]
    # Create the draft payment    payment_id = self.execute_kw('account.payment', 'create', [{        'communication': 'Payment for %s' % invoice["display_name"].strip(),        'company_id': invoice["company_id"][0],        'partner_id': invoice["partner_id"][0],        'payment_method_id': payment_method["id"],        'journal_id': journal["id"],        'name': invoice["display_name"],        'partner_type': 'customer',        'amount': amount,        'payment_type': 'inbound'    }])