How to validate a string literal type using zod

I commented that this might be a duplicate since the core of the question could be solved with z.literal, but it is a bit different. Just to illustrate what you can do:

import { z } from 'zod';
const PaymentTypeSchema = z.union([
  z.literal('CHECK'),
  z.literal('DIRECT DEPOSIT'),
  z.literal('MONEY ORDER'),
]);
type PaymentType = z.infer<typeof PaymentTypeSchema>;

const schema = z.object({
  paymentType: PaymentTypeSchema,
});

A simpler approach than this is to use the z.enum helper which removes some of the boilerplate:

const PaymentTypeSchema = z.enum(["CHECK", "DIRECT DEPOSIT", "MONEY ORDER"]);
const schema = z.object({
  paymentType: PaymentTypeSchema,
});

Alternatively, you can make PaymentType into an enum and use z.nativeEnum to parse the values like:

enum PaymentType {
  Check = 'CHECK',
  DirectDeposit="DIRECT DEPOSIT",
  MoneyOrder="MONEY ORDER"
}

const PaymentTypeSchema = z.nativeEnum(PaymentType);
const schema = z.object({
  paymentType: PaymentTypeSchema,
});