Use promotion codesBeta

curl https://api.stripe.com/v1/promotion_codes \
  -u "
sk_test_4eC39HqLyjWDarjtT1zdp7dc
:" \
  -d coupon={{COUPON_ID}} \
  -d code=VIPCODE

const session = await stripe.checkout.sessions.create({
  line_items: [
    {
      price_data: {
        currency: 'usd',
        product_data: {
          name: 'T-shirt',
        },
        unit_amount: 2000,
      },
      quantity: 1,
    },
  ],
  mode: 'payment',
  ui_mode: 'custom',
  return_url: '{{RETURN_URL}}',
  allow_promotion_codes: true,
});

import React from 'react';
import {useCustomCheckout} from '@stripe/react-stripe-js';

const PromotionCode = () => {
  const {applyPromotionCode, removePromotionCode} = useCustomCheckout();
  const [draft, setDraft] = React.useState('');
  const [loading, setLoading] = React.useState(false);

  const handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
    setDraft(e.target.value);
  };
  const handleSubmit = () => {
    setLoading(true);
    applyPromotionCode(draft).finally(() => {
      setDraft('');
      setLoading(false);
    });
  };
  const handleRemove = () => {
    removePromotionCode();
  };

  return (
    <div>
      <input type="text" value={draft} onChange={handleChange} />
      <button disabled={loading} onClick={handleSubmit}>
        Apply
      </button>
      <button onClick={handleRemove}>Remove</button>
    </div>
  );
};

export default PromotionCode;