Do I need a store on a marketplace or my own website before applying for a VAT number?
You must be ready to operate in the country where you're registering for VAT before you apply.
Some countries require screenshots of your shop or seller profile (if you’re selling on Amazon, for example) as evidence you need the VAT number. Without it, your application will be rejected.
Even if you’re not required to provide such evidence to register, you need to be ready to start selling once you get your VAT number. If you don’t show sales after the VAT number has been issued, the tax authority will remove you from the VAT register.