To find your unique Transaction Hash ID, immediately after making your payment, find the transaction you just completed, then click on the circle with a > inside of it. You will find it next to the date.
When you click on the circle, the page will open a little and you will see a little box with an arrow pointing to the right... click on the box (verify on the Blockchain).
When the page comes up, it will show your unique Transaction Hash ID, for the transaction you just made. It is the first long series of numbers and letters (in blue) right under the page title "Transaction."