Hi Jk.
If your frog isn't skinny as hell, you don't need to worry. Just check humidity and heat. Try different food items. I got two adults last year who refused to eat aswell. They did not eat for almost 3 months and were still fine. So changed the subtrate. I started keeping them on water only(just check If you need to condition your water), which I changed every other day. You could literatly see them getting fitter. I tried different food. They seem to love fish. Nowadays they are eating almost everything(own fingers included ).
So don't worry TOO much.
If you tongue feed you could start to "annoy" him a bit - just poke his mouth and feet with the food item.

Good luck buddy

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