You can create an invoice to send to your buyers from your selling dashboard. Click on the "Selling" link in the upper left-hand corner of any page. On the navigation toolbar to the left side of your selling dashboard, click the "Orders" tab, then select "Create invoice."
Once on that page, select the item(s) you would like to include in the invoice from your inventory list and click the "Add items to invoice" button. Start typing the buyer's username in the "Send invoice to" field and select the appropriate username from the drop-down. Enter the total price, including any shipping, tax and discounts; this is the final amount that the buyer will pay for all items included in the invoice.
After you have specified all the details for your offer, click the "Send invoice" button to notify the buyer.
Please note that the buyer will not be required to accept the proposed price and may choose to deny the offer. Should the buyer accept, they will be able to complete checkout via the payment method(s) you have set up in your booth.