Horizontal nipples?
Nipple and/or Cup waterer training can be challenging indeed.
I've had 2 day old chicks figure it out in a couple hours and older birds taking much longer to 'get it'.
You
do need to remove
all other water sources, and this should not be done during extreme heat or cold as you don't want to risk dehydration.
Just keep tapping the button and eventually they'll get it, could take an hour, could take a week.
Sometimes grabbing their head and tapping the button with their beak works, sometimes it just freaks them out.
Patience and perseverance, like other thing with chickens, is definitely needed with the nipple waterer 'training'.