The payment gateway is an online e-commerce application service provider that securely authorises credit card or direct payments processing for e-commerce
Ask your designer what type of payment gateway is used. Go for a more trusted known brand like Eway, Paypal or Stripe for conversion.
Then investigate what plan you will be on. This will tell you the transaction costs so you can work out your sales costs. Ask how long it takes the funds to land into your account. The quicker, the better so you can ship your items as quick as possible.