If i sell good in the uk with fba i must be vat register. But would i have to be vat register in Ireland when good don’t land here
I would advise you to contact a professional tax advisor who would help you clarify whether you need to register for the VAT in Ireland as well or not.
If you are a UK or EU Seller, then goods sold on any UK / EU website to deliver in Republic of Ireland is ok. You just pay VAT in the country of the website sold on, eg UK is sold from amazon.co.uk
To note after Brexit, that will change if sold from the UK website to anywhere in the world, it will then be no VAT charged and the Buyer will need to pay customs duty etc (the same as sending outside the EU at the moment)