How does SumUp work? SumUp offers payments services to help businesses receive payments in store, online and on the go. It is probably best known for its card reader devices, but it can also help with businesses needing to create ecommerce sites, manage invoices and with a business payment card. SumUp offer three card reader devices to help your business accept credit card and contactless payments. SumUp Air connects to your smartphone or tablet through Wifi and you can use a free App to manage your payments. This device can make up to 500 transactions on a single charge. Businesses can also add a cradle to the SumUp Air that will show your customers that you are ready to accept card payments.