Hello fellow travelers,
This is a reminder that the UK is NOT part of the European Union anymore since Brexit. This means that if you go to the UK, you must scan your barcode at the French customs office when leaving France.
If you fail to do this and later travel to another European country or return to France before heading home, you can attempt to validate your tax refund in the next EU country you visit. However, customs officers may refuse to validate it if you have already left the EU with the goods.