Also called: Application Programming Interface
What an API is
An application programming interface, or API, is a contract between software systems. It defines what one system can request, the format for that request and what response to expect. The API exposes specific data or functions without revealing how the other software works internally.
For example, a scheduling tool could request staff hours from a payroll system through an API instead of requiring you to enter the hours twice. Web APIs commonly use HTTP to send requests and return data in formats such as JSON or XML.
An API connects software systems, but it does not tell you what the connection costs or how securely it is configured.
How an API works
A system sends a request to an API endpoint, which is a defined address for a function such as retrieving a record or submitting an update. The request can include data and credentials. The receiving system returns the requested information or an error, so the connected software can show a result or take another action.
An API connection depends on rules for access and handling requests. Authentication checks who is making a request, while authorization determines what that user or system can do. Input validation and error handling help prevent bad data or failed requests from disrupting connected work.
How APIs relate to payments
A payment API is a specialized API that lets software communicate with payment services. A website or app can send transaction details, such as an amount and payment method, and receive a result such as an approval, rejection or transaction ID. The payment provider and its connected payment systems handle the processing behind that request.
The general term API does not mean a payment fee, payment network or bank transfer. API access and payment processing are separate concepts, and the API name alone does not tell you what a provider charges. You will not find one standard API fee or statement label that applies across businesses.
What you can actually change
An API does not automatically lower your payment costs. You can control which systems you connect, what information passes between them and how you handle access, errors and sensitive data.
- List the specific task each integration must perform, such as sending a payment result to your accounting system.
- Limit access to the data and functions each connected system needs.
- Build error handling for rejected requests, timeouts and unexpected responses so a failed request does not create a missing record or duplicate action.
- For payment integrations, identify where card data enters your systems and whether a hosted payment form can keep it out of your environment.
- Map the workflow. Write down what information should move between each pair of systems and which system owns the record.
- Limit system access. Give each integration credentials and permissions only for the data and actions it needs.
- Test failure cases. Before launch, test rejected requests and timeouts to confirm your software records the problem without repeating an action.
Frequently asked questions
What does API stand for?
API stands for Application Programming Interface. It is a defined set of rules that lets one software system request data or functionality from another, including rules for requests and responses.
Is an API the same as a payment API?
No. API is the general term for a software interface. A payment API is a specific kind used to connect software with payment services, such as when a website submits a payment request and receives its result.
Does an API charge a fee?
API is a technical term, not a standard fee name. A provider can set charges for its services or API access, but the API label alone does not tell you the price or how it appears on a statement.