Apistogrammas mostly refuse to eat dry foods, I would therefore recommend frozen brine shrimp or live food. Apistogrammas come from dense areas with lots of leaves and low light. They like to hide if they don’t feel secure. I’ve had apistos hide for over a month before they felt secure enough to come out all day.
My experience is that the more hiding places you have, the more they are out in the open. If they know they can hide any second they want they feel secure enough the swim out in the open. If they only have 1 or 2 hiding places, they will keep hiding.
For example my 60 liter tank contains 4 small apistogramma sp. D37. This tank is heavily planted with about 12 savu pods and 2 coconuts to hide in, combined with lots of wood structures and lots of dead leaves covering the savu pods and coconuts. They are always out in the open, but once I scare them by taking of the lid, they hide in a second. Then I proceed to put the food in and close the lid. Within a second they are out in the open again and eating. I think this is the most natural behaviour for them.