[mw48]

Does anyone know a character or input for a textbox that messes with java?

[sexyPudding]

is there money involved?
how do you the backend is java?
the way it's done is sending requests to the same endpoints but customized to exploit it

dont look at the inputs on the website. look at where the data is sent

[Vana]

Try the various control characters.

Additionally, if input size isn't limited you may be able to throw a MemoryError by sending a large string.