It is not greyed out for me.
It may be that for some reason you can't buy from that seller.
If you have unpaid strikes you could be blocked or if you have used that seller before and they blocked you. Are you in mainland UK? Some sellers block buyers from NI, Highlands & Islands etc.
I assume you have put a quantity in to buy.
All you can really do is find another seller. Sorry.
To be completely honest, I would avoid that seller anyway. They are trading (buying items to sell) on a private account which means you have to pay the buyer protection fee and they don't pay Ebay their fees.
