This is my code changes:

class account_register_payments(models.TransientModel):

    _inherit = "account.register.payments"

    @api.model

    def default_get(self, fields):

        """This method is to create payment for multiple

        vendors and also check whether the shipment or

        invoice in return or refund state. If there it will

        raise popup based on shipment and invoice returns

        :rtype dict

        :return returns the payment value"""

        rec = super(account_register_payments, self).default_get(fields)

        context = dict(self._context or {})

        active_model = context.get('active_model')

        active_ids = context.get('active_ids')

        # Checks on context parameters

        if not active_model or not active_ids:

            raise UserError(_("Programmation error: wizard action executed \

                            without active_model or active_ids in context."))

        if active_model != 'account.invoice':

            raise UserError(_("Programmation error: the expected model for this \

                            ' action is 'account.invoice'. \

                            The provided one is '%d'.")

                            % active_model)

        # Checks on received invoice records

        invoices = self.env[active_model].browse(active_ids)

        for invoice in invoices:

            partner = invoice.partner_id.id

            stock_picking = self.env['stock.picking'].search(

                [('partner_id', '=', partner)])

            for picking in stock_picking:

                if (picking.return_doc is True and picking.state != 'done'):

                    raise UserError(_("Some shipment are in return stage, \

                                    Please complete it"))

            invoice_return = self.env['account.invoice'].search(

                [('partner_id', '=', partner)])

            for inv in invoice_return:

                if(inv.type == 'in_refund'):

                    raise UserError(_("some of the invoices are in return state, \

                                    have to complete it"))

        if any(invoice.state != 'open' for invoice in invoices):

            raise UserError(_("You can only register payments \

                            for open invoices"))

        # =======================================================================

        # if any(inv.commercial_partner_id != invoices[0].commercial_partner_id for inv in invoices):

        # raise UserError(_("In order to pay multiple invoices at once, \

        # they must belong to the same commercial partner."))

        # =======================================================================

        if any(MAP_INVOICE_TYPE_PARTNER_TYPE[inv.type] != MAP_INVOICE_TYPE_PARTNER_TYPE[invoices[0].type] for inv in invoices):

            raise UserError(_("You cannot mix customer invoices and \

                            vendor bills in a single payment."))

        if any(inv.currency_id != invoices[0].currency_id for inv in invoices):

            raise UserError(_("In order to pay multiple invoices at once, \

                                they must use the same currency."))

        total_amount = sum(inv.residual * MAP_INVOICE_TYPE_PAYMENT_SIGN[inv.type] for inv in invoices)

        communication = ' '.join([ref for ref in invoices.mapped('reference') if ref])

        rec.update({

            'amount': abs(total_amount),

            'currency_id': invoices[0].currency_id.id,

            'payment_type': total_amount > 0 and 'inbound' or 'outbound',

            'partner_id': invoices[0].commercial_partner_id.id,

            'partner_type': MAP_INVOICE_TYPE_PARTNER_TYPE[invoices[0].type],

            'communication': communication,

        })

        return rec

the bold things are my code changes but it doesn't works me because it calls the original one.

How can i rectify this..

Hi silviaa,

It seems you are using same class name as original . Please refer original code

https://github.com/odoo/odoo/blob/447c2770b0b3b809d822b2e1acfaba95777be70d/addons/account/models/account_payment.py

can you please change class name and try. I cannot see any changes in this method. Its totally same as original. 

Thanks

Chandran Nepolean