Hi,

If you need to get the current order while validating the payment, you need to extend the payment validate function, check the code below,
by using this.env.pos.get_order() we can get the current order.

odoo.define('module_name.PaymentScreen', function(require) {
    'use strict';
    const PaymentScreen = require('point_of_sale.PaymentScreen');
    const Registries = require('point_of_sale.Registries');
    const session = require('web.session');

    const InvoicePaymentScreen = PaymentScreen =>
        class extends PaymentScreen {
            setup() {
                super.setup();
            }

            async validateOrder(isForceValidate) {
                const order = this.env.pos.get_order();
                console.log(order,"Current order")
                await super.validateOrder(isForceValidate);

                    //add your code here.
                }
            }
        };

    Registries.Component.extend(PaymentScreen, InvoicePaymentScreen);

    return PaymentScreen;
});

Hope it helps