Amphibeans can not see objects that do not move, so they will generally not eat objects that do not move. Even slow mowing preys like different kind of worms can be "slow moving" enough for frogs to ignore. I've read that RETF seldomly eat worms, However, I can not comfirm this myself, since I have not tried.
The most common food for RETF are crickets, which they can be feed on as a staple diet, as long as the crickets are powderd with the right supplements. Blaptica dubia (a common, easy to breed cockroach) is also good food, even better than crickets from a nutrion point of view. They get quite large, so only juveniles of correct size can be used.