@api.onchange('partner_id', 'pay_now')

    def onchange_partner_id(self):

        pay_journal_domain = [('type', 'in', ['cash', 'bank'])]

        if self.pay_now != 'pay_now':

            if self.partner_id:

                self.account_id = self.partner_id.property_account_receivable_id \

                    if self.voucher_type == 'sale' else self.partner_id.property_account_payable_id

            else:

                account_type = self.voucher_type == 'purchase' and 'payable' or 'receivable'

                domain = [('deprecated', '=', False), ('internal_type', '=', account_type)]

​

                self.account_id = self.env['account.account'].search(domain, limit=1)

        else:

            if self.voucher_type == 'purchase':

                pay_journal_domain.append(('outbound_payment_method_ids', '!=', False))

            else:

                pay_journal_domain.append(('inbound_payment_method_ids', '!=', False))

        return {'domain': {'payment_journal_id': pay_journal_domain}}