External Purchase: status 401

Good morning, I am configuring in backend the sending of reports regarding purchases made in app with external platform (Stripe) as per documentation. To be clear I am talking about ExternalPurchase. However, when I make the call it returns "Apple responded with status 401". I verified the token on jwt.io as per documentation and it is working. I don't understand where I am going wrong. Below I share the code with you:

const express = require("express");
const bodyParser = require("body-parser");
const jwt = require("jsonwebtoken");
const fs = require("fs");
const app = express();
const https = require("https");

const APPLE_KEY_ID = "XXXXX";
const APPLE_ISSUER_ID = "***-***-***-xx-xxxxxx"; 
const APPLE_PRIVATE_KEY = fs.readFileSync("AuthKey_xxxxx.p8", "utf8"); 
const APPLE_AUDIENCE = "appstoreconnect-v1";

function generateAppleJwt() {
  const now = Math.floor(Date.now() / 1000);
  const payload = {
    iss: APPLE_ISSUER_ID,
    iat: now,
    exp: now + (5 * 60), 
    aud: APPLE_AUDIENCE
  };

  return jwt.sign(payload, APPLE_PRIVATE_KEY, {
    algorithm: "ES256",
    header: {
      alg: "ES256",
      kid: APPLE_KEY_ID,
      typ: "JWT"
    }
  });
}

app.post('/webhook', bodyParser.json({ type: 'application/json' }), async (req, res) => {
  let eventType = req.body.type;


  const relevantEvents = [
    "invoice.paid"
  ];

  if (relevantEvents.includes(eventType)) {
    try {
      const data= req.body.data;
      const platform = data.object.subscription_details.metadata.platform;
      
      if (platform === "IOS") {
        const token = generateAppleJwt();
       
        const applePayload = {
            appAppleId: "xxxx",
            bundleId: 'com.***.***.test',
            externalPurchaseId: data.object.id,
            purchaseTime: new Date(data.object.created * 1000).toISOString(),
            purchaseAmount: {
                amount: (data.object.total / 100).toFixed(2), 
                currencyCode: data.object.currency.toUpperCase()
            },
            purchaseLocation: {
                isoCountryCode: "IT" 
            }
        };

        const jsonString = JSON.stringify(applePayload);
        const agent = new https.Agent({ keepAlive: false });

        const response = await fetch(
          "https://api.storekit-sandbox.apple.com/externalPurchase/v1/reports",
          {
            method: "PUT",
            headers: {
              Authorization: `Bearer ${token}`,
              "Content-Type": "application/json",
              "Accept-Encoding": "identity",
            },
            body: JSON.stringify(applePayload),
          }
        );

        if (!response.ok) {
          const errorText = await response.text();
          throw new Error(
            `Apple responded with status ${response.status}: ${errorText}`
          );
        }

        console.log("✅ Notifica inviata ad Apple con successo");
        
      } else {
        if(!canSendNotification){
            console.log("Non è una Sub. Nessuna notifica inviata.");
        }else{
            console.log("Customer non iOS. Nessuna notifica inviata.");
        }
      }

    } catch (err) {
      console.error("Errore durante l’invio ad Apple:");
        if (err.response) {
            console.error("Status:", err.response.status);
            console.error("Headers:", err.response.headers);
            console.error("Data:", err.response.data);
        } else {
            console.error("Message:", err.message);
        }
    }
  }

  res.status(200).send("OK");
});

exports.checkSubStripe = functions.https.onRequest(app);