Please use relevant case law in NSW Australia to assist.

Tony is a 16-year-old student working at Dominos as a delivery assistant. He uses his phone to navigate his way when delivering food orders. During a basketball game, his phone got broken. As the phone is an essential tool for his work, he decides to replace it immediately. On getting to Fi-Hi BJ, he locates the section where iPhones are placed, calls for the help of a sales assistant and picks out an iPhone 14 priced at $1500. On getting to the counter, Tony hands the phone to the cashier and is told it costs $1500. He swipes his card and is given the phone pack with his receipt. On getting home, he opens the pack and discovers a small crack on the screen. The crack does not affect any functionality of the phone, but Tony is angry about the crack and alleges that after spending $1500, the crack means that the contract between himself and JB Hi-Fi is invalid.

i. Advise Tony whether there is a valid contract between himself and JB Hi-Fi.

ii. Advise Tony on available options with regards to the small crack on the screen.

Assuming Tony's phone did not get broken, and it was functioning perfectly, and Tony negotiates the sale of an iPhone 14 with JB Hi-Fi (on a buy now and pay later deal) but Tony fails to pay for the phone arguing that he lacks the requisite capacity to contract;

iii. Can Tony refuse to pay based on his argument? NOTE: Please refer to ONLY case law. Do not refer to any statutory provisions