# Agreement

**Agreement** is a smart contract that tracks how many **Certificates** were delivered from a **buyer** to a **seller**.

It implements the `onERC1155Received` interface and detects when a Certificate is sent to the agreement, then immediately forwards it to the buyer and accounts for the delivery.

Once the Agreement is fulfilled, it can no longer receive Certificates tokens.

![](/files/XDvq7jyUOkgBXD27Ifu2)


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