# 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!&#x20;

🚧 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!&#x20;