.reduce not working properly

I pretty sure i’m implementing the .reduce method wrong. Can someone tell my what i’m doing wrong?
I’m trying to the sum when a new expense is added to the array and i’m displaying it under the expense category.

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You’re implementing it correctly. The only catch you might be getting - .reduce() has to have second argument, initial value when called with empty array, otherwise error will be thrown:

const array = [1, 2, 3];
const empty = [];

array.reduce((a, b) => a + b); // 6
empty.reduce((a, b) => a + b); // Error

empty.reduce((a, b) => a + b, 0); // 0