taxpayer identification number

Hello,
I have a general question regarding invoices
I'm working on B2B contract as a programmer, for that i needed to become sole proprietor and have my own accountant to which im providing all invoices every month.
I can send her only invoices from products that are connecting to what im doing, meaning they could be invoices from buying keyboard, mouse etc.
Such invoice need to have my taxpayer identification number. Im VAT-EU payer.
I remember i wanted to buy something from Razer website and needed that on the invoice and that time, Razer support was telling me that there is some EU-directive which don't allow them to do that. Can i ask what directive was that?
Sorry for this question but in Poland if i want to buy something to my work, they always have to add my taxpayer identification number to the invoice so im wondering whats the difference with that outside of Poland.