How to contact the buyer as a seller and how to contact the seller as a buyer are the same. Here we demonstrate how to contact the buyer as an example:
How to Contact Buyer/Seller (on the Web)
After an order gets filled, it can be found in Fiat [Order] - [Pending] or [Completed] orders. Find the order and click [Chat] to start a chat in the box on the left.
How to Contact Buyer/Seller (on the App)
After the order is successfully matched or completed, go to the Fiat Trading page, click [Orders], and select either [Pending] or [Completed]. Find the corresponding order and enter the order details page, where you can click the [Chat] icon on the right to start a chat.

