If you are unsure about your Tax Identification Number (TIN), the information can typically be found on official documents such as income tax returns from your country of residence, government-issued identification cards, or correspondence from the respective country's tax authorities.

You can also contact the tax authorities in your country of residence to get information about your TIN. You can find further information about how to locate your TIN here if you live in and EU/EEA country and here if you live in a non-EU/EEA country.