> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://amer.developers.trustly.com/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://amer.developers.trustly.com/_mcp/server.

# API fundamentals

Trustly's API uses OAuth for authentication and cryptographic signatures for request integrity. Use the sandbox environment to test your integration before going live.

OAuth login authorization flows for bank-side authentication.

Generate and validate cryptographic signatures for API requests.

Prevent duplicate operations with unique merchant references.

Use the sandbox environment and demo banks to simulate transactions.