What it is
A bank or payment-company service (YooKassa, T-Business, CloudPayments, Robokassa) through which a site accepts card and instant payments. The buyer pays on the provider's secure page, the money lands on the merchant's account, the provider keeps a 1–3 % fee. A payment system of your own needs a licence and certification, so almost nobody builds one: every shop connects a ready-made provider.
How we use it
On sites and in bots we connect a ready-made provider by its documentation: you sign the contract with the provider, we set up payment, receipts and order notifications. We do not build payment systems of our own.