Payment aggregators (aka third party processors) are service providers that allow other businesses to accept credit cards without having to set up a merchant account. They make money by taking a percentage of credit card sales and also a transaction charge.
Payment aggregators are a business on their own. They need to get approved for a merchant account to support their business to split up that merchant account to many businesses. It takes a deeper underwriting process, but they are supported and Clearly Payments does offer merchant accounts for payment aggregators.
Payment aggregators can provide some great services and you can investigate further on the differences between a merchant account and an aggregated account.