A payment service is a combination of a payment gateway and a merchant services offering
In order to process a transaction (to charge a card), a merchant needs a merchant account (through which payments are processed and deposits are executed) and a payment gateway (to submit transactions for processing). Payment service companies will normally provide a way for a merchant to get a merchant account, and will also supply a hosted payment gateway that a merchant could use to process transactions.
As you have, probably, noticed by now, UniPay is not exactly a provider of online payment services. There are many payment service companies, however, which utilize UniPay technology and offer both merchant services and hosted access to UniPay gateway. Contact us to get the list of such companies.