VAT is based on location, you can set up the VAT information when you add your billing information, then select your country, the VAT field will appear if it is applicable:
If your billing is already set up, then you will need to sign in to your account here:
Type in your account email and password for Backblaze then click the sign in button.
Click the Billing link in the left-hand navigation panel.
Then click update payment method.
When you choose the country it will prompt for the VAT number:
Enter your country code and your VAT number to attach the VAT number to your account.
If you are creating a group, once you create the group and go to step 2, you will be asked for the VAT number, and if you have a group set up, then you can click on the Edit link in the group next to payment section, then add the VAT number here.
For more information on VAT formats please go here.
If you would like to know the rate for your EU country please see here: