Pacman frogs are finicky that way. Here's what I suggest. Get him a shallow water bowl, make it take up most of the terrarium space. A good idea is a plant saucer (you know those plastic things that go under plant pots). Put him in it for a few hours. Now dangle half a nightcrawler in front of him on some tweezers. Don't wave it at him, just let it squirm. If he doesn't go for it in a minute or so, drop it in the water bowl with him. The squirming action is great for getting these guys to eat. If you try this, let us know how he gets on.

As has been stated earlier, they don't take to Dubia roaches easily. I had problems doing this with small pacman frogs.