Which domain should I use when setting up a new market

Hey!

My store is based in the UK. I have recently set up a new market in Ireland but I’m unsure which domain setting I should use.

The Primary Domain only, Domain or subdomain or subfolders.

I currently have it set as subfolders and the domain is Baby & Nursery | Premium Products for Your Little One

I was told by a customer in Ireland that they were unable to select the add to cart button when using both bundlebabyonline.com and Baby & Nursery | Premium Products for Your Little One on safari on mobile. Could the domain be the issue?

Does anyone know the differences between the 3 types of domains available in markets and which one I should be using for my Ireland site?

Thanks!