Once you're done shopping, just go in your refund, and on the third step click on the button to ask for the barcode.
THE BARCODE IS PART OF THE TAX FREE FORM.
GENERATING THE BARCODE WILL LET YOU DOWNLOAD THE WHOLE FORM IF YOU NEED TO PRINT IT. (MANDATORY IF YOU VISIT AN OTHER EU COUNTRY BEFORE LEAVING)
THE TAX FREE FORM WILL ALSO BE SENT TO YOUR EMAIL.
It usually takes a couple minutes to generate (it's being processed by the french customs).
You will also get in on your email once its generated