If you have a UID number, you should click on "Business Purchase" after the checkout - then you can enter the UID number as well as the correct address and receive the invoice without VAT.
But this can only be done during the initial checkout process.
You may need to put your Country Code before the VAT number for it to be recognised.
As below, ensure you check out - do not use Payal Express Checkout for business purchases.
Ensure you change to Business purchase.
Then enter your VAT number. Please cover over the "i" for help on how to enter.