Every teenage does the same thing. It's up to the parents to hold their fort. Every time this happens we would struggle with ourselves and with them.Don't want to say NO outright, afraid hurt their feelings, or make them think we don't love them. Don't want to say YES too easily because we are not rich enough to throw money around, or spoil them.
So, if we'll discuss why they need it. If it's reasonable we'll say yes. Otherwise we'll say no. If they fight back saying why other people's kids have so and so but not me? Then we'll say: we have different priorities. We don't buy fancy toys but we do more sports or travel......
Be firm but calm when talking to him.