# APIs to build a transaction This type of integration is where we call your API (e.g. \`marketplace.com/buildTx\`) and your API returns a transaction for us to sign! This is the most common type of integration! 🚧 Coming soon - a self serve dashboard for you to integrate on your own! These are the chains we currently support for this type of integration: * ETH * MATIC * SOL * ADA * XTZ * AVAX * BNB At a high level, your API should take in a few things (passed in this format): * `tokenId` * `contractAddress` * `quantity (optional)` We then expect a complete **unsigned** transaction back, which we will then sign and submit using our own RPC! To get started, email us at `marketplaces@usewinter.com!` ### What does the API need to take and what does it need to return? At a high level, your API should accept: * `tokenId` * `contractAddress` * buyerWalletAddress It should then take this and return back a built transaction for us to sign. Generally, you'll also need this type of transaction to send to a wallet, like Metamask! --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.usewinter.com/marketplace-integrations/implementation-strategy/apis-to-build-a-transaction.md?ask= ``` The question should be specific, self-contained, and written in natural language. 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.