Javascript – SyntaxError: No number after minus sign in JSON at position 1 (line 1 column 2) through POST request in Postman

When I use my API on my website application it works perfectly fine, however when I try testing it in Postman I get SyntaxError: No number after minus sign in JSON at position 1 (line 1 column 2). I’ve put the data into the body in Postman and made sure that the names are correct but the error still persists. The weird thing is, I only get this with POST request. My GET and DELETE requests work fine from Postman. The JSON response after adding the product to the basket from the website is:

{
id: 70,
productId: 21,
userId: 10,
size: ‘Medium’,
customerQuantity: 1
}

But when I use postman put the required data in body it gives the error in the title

The API code:

import prisma from "@/app/prismadb";
import { NextResponse } from "next/server";

export async function POST(request: Request) {
    const body = await request.json();
    const { productId, userId, size, customerQuantity } = body;

   

    try {
        const existingCartItem = await prisma.basket.findFirst({
            where: {
                productId,
                userId,
                size: {
                    contains: size, 
                }
            },
        });

        if (existingCartItem) {
            await prisma.basket.delete({
                where: {
                    id: existingCartItem.id,
                },
            });
        }

        const product = await prisma.basket.create({
            data: {
                productId,
                userId,
                size,
                customerQuantity
            },
        });

        return NextResponse.json(product);
    } catch (error) {
        console.log("Error adding product to cart", error);
        return NextResponse.error();
    }
}

export async function DELETE(request: Request) {
    const body = await request.json();
    const { productId, userId } = body;

    try {
        const deleteItem = await prisma.basket.deleteMany({
            where: {
                productId: productId,
                userId: userId,
            },
        });

        return NextResponse.json(deleteItem);
    } catch (error) {
        console.log("Error deleting product", error);
        return NextResponse.error();
    }
}