I checked your account and can see that you have already filled-in your W-8BEN form. On your Tax Information page, you are also being requested to add your VAT information.
Upwork charges the country-specific Value Added Tax (VAT) to freelancers and agencies in the European Union (EU), unless you provide a valid VAT number. VAT will be assessed on services provided by us, not on services you provide your clients. You may read more about EU Value Added Tax (VAT) here.