Why does the rate keep refreshing?

Before you confirm

The quote refreshes every few seconds so the rate you see is current. The countdown shows when the next refresh happens.

After you confirm

In ticket mode the rate is held for a short window while your deposit arrives. The window and the accepted amount range are shown on the ticket.

If the window passes

A deposit that arrives later is quoted again at the current rate. If that fails, it goes back to your refund address.