> For the complete documentation index, see [llms.txt](https://docs.ecommerce.seb.ee/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ecommerce.seb.ee/integration/api-client-sdk.md). # API Client SDK Integrate the Merchant API with typed, server-side SDKs across multiple languages. The **API Client SDK** provides server-side libraries for integrating with the **Merchant API**. The SDK simplifies backend development by handling common integration tasks such as OAuth 2.0 authentication, JWE card data encryption, HTTP communication, JSON serialization, and webhook processing. Instead of working directly with raw REST requests, developers can use strongly typed, language-specific SDKs to integrate payments and other gateway services. The SDK is available for: * Java * PHP * C# / .NET * Node.js / TypeScript *** ### Documentation Structure This section contains everything required to integrate using the API Client SDK. #### Overview Learn about the SDK architecture, supported languages, API coverage, supported environments, and implementation responsibilities. #### Quickstarts Install the SDK, configure authentication, and create your first Sandbox payment using your preferred programming language. Available Quickstarts: * Java * PHP * C# / .NET * Node.js / TypeScript #### Using the SDK Step-by-step integration guides covering common SDK operations, including: * Creating payment requests * Processing payment responses * Handling errors * Receiving webhook notifications * Working with refunds and payment operations #### Guides Cross-language documentation covering: * Error Handling * Security Mechanics * Architecture & Extensibility * Overriding SDK Adapters *** ### Getting Started If you are new to the SDK, we recommend the following learning path: 1. Read the [**Overview**](/integration/api-client-sdk/overview.md). 2. Complete the [**Quickstart**](/integration/api-client-sdk/quickstarts.md) for your programming language. 3. Continue with [**Using the SDK**](/integration/api-client-sdk/using-the-sdk.md). 4. Explore the [**Guides**](/integration/api-client-sdk/guides.md) for advanced topics and best practices. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://docs.ecommerce.seb.ee/integration/api-client-sdk.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.