CORS error when using Cloud Functions for Firebase - node.js

Question

This is my first question posed, so I apologize if it is not formatted well.
I have been trying to figure out how to deal with the following CORS error, as well as, the CORS preflight error:
...has been blocked by CORS policy: The 'Access-Control-Allow-Origin' header has a value 'https://example.com/' that is not equal to the supplied origin.
I have spent the last few days reading every question on this topic, and all other documentation I could find on CORS/Cloud Functions/Axios/etc. I am using React, Node, Express, Axios, Google Firebase to host, and Google Cloud Functions.
I am trying to access the PayPal API to gain a bearer token to make further API requests. I understand some of the code pertaining to the request headers might be redundant. I have just been trying to throw anything at this.
Does anyone have any ideas?
The node file - index.js
const axios = require("axios");
const express = require("express");
const cors = require("cors")({ origin: true });
const app = express();
app.use(cors());
app.use(express.json());
app.post("/v1/oauth2/token/", cors(), (req, res) => {
res.set("Access-Control-Allow-Origin", "https://example.com/");
var data = qs.stringify({
grant_type: "client_credentials",
});
var config = {
method: "post",
url: "https://api-m.sandbox.paypal.com/v1/oauth2/token/",
headers: {
"Access-Control-Allow-Origin": "https://example.com/",
Authorization:"xyz",
"Content-Type": "application/x-www-form-urlencoded",
},
data: data,
};
axios(config)
.then(function (response) {
let bearerToken = response.data.access_token;
res.status(201).send(bearerToken);
})
.catch(function (error) {
console.log(error);
});
});
exports.api = functions.https.onRequest(app);
The react file - payment.js
import axios from "../axios/axios";
const oneTimePaypalPayment = async () => {
const response = await axios.post("/v2/checkout/orders");
console.log(response);
};
The axios file - axios.js
import axios from "axios";
const instance = axios.create({
headers: {
"Access-Control-Allow-Origin": "https://example.com/",
"Access-Control-Allow-Headers": "https://example.com/",
},
baseURL: "https://us-central1-example.cloudfunctions.net/api/"
});
export default instance;
What I have tried
I have tried using the wildcard " * " just to try to get it to work but no luck. I read on another answer that Google Cloud Functions do not recognize the '*' anyways. I have also tried all of the code below, and a lot of other ways to manipulate the Access-Control-Allow-Origin on the request header
const allowCrossDomain = function (req, res, next) {
res.header("Access-Control-Allow-Headers", "*");
res.header("Access-Control-Allow-Origin", "*");
res.header("Access-Control-Allow-Methods", "GET,PUT,POST,DELETE");
next();
};
app.use(allowCrossDomain);
app.all("*", (req, res, next) => {
res.header("Access-Control-Allow-Headers", "*");
res.header("Access-Control-Allow-Origin", "*");
res.header("Access-Control-Allow-Methods", "GET,PUT,POST,DELETE");
next();
});
const corsOptions = {
origin: "https://example.com/",
};
app.use(cors(corsOptions))
app.options("/v1/oauth2/token", cors(corsOptions));
app.use(cors({origin:true}));
Any thoughts would be greatly appreciated

Answer 1

In a cloud function that you are exporting or working with use below for Origin :
exports.your function = async (req, res) => {
res.set('Access-Control-Allow-Origin', '*');