How can I save request from client on server - api

Question

So basically I have a api route when I request the data from client and send the data from the client that sent the request to another client. Concretely I have student user that has bought a course and I want to notify the teacher when the course is bought. When student buys lesson he sends his user_name and other data which I want to save on server and then send the data from user that sent it to the teacher.
Here is code for the
import { NextApiRequest, NextApiResponse } from "next";
export default async function handler(
req: NextApiRequest,
res: NextApiResponse
) {
res.setHeader("Access-Control-Allow-Origin", "*");
const { user_name, course_id, author_id, courseName } = req.body;
const author = await fetch(
`http://localhost:8000/api/user-id/${author_id}`
).then((res) => res.json());
console.log(author.user);
const message = `Hi ${author?.user?.name}, ${user_name} has purchased your course:
${courseName}!`;
res.status(200).json({
message: {
message: message,
courseName: courseName,
buyerName: user_name,
authorName: author?.user?.name,
},
});
This is the api call from student
const handleSendMessage = async () => {
const res = await fetch(`http://localhost:3000/api/puchase-message`, {
method: "POST",
headers: {
"Content-Type": "application/json",
// disable preflight request
"Access-Control-Allow-Origin": "*",
},
body: JSON.stringify({
user_name: session?.user_name,
course_id: session?.product_id,
author_id: user_id,
courseName: session?.productName,
}),
});
};
This is api call for the teacher to get the message
const fetchMessage = async () => {
const res = await fetch(`http://localhost:3000/api/puchase-message`, {
method: "GET",
headers: {
"Content-Type": "application/json",
// disable preflight request
"Access-Control-Allow-Origin": "*",
},
});
const data = await res.json();
setMessage(data.message);
};
This is the output