Sandbox User Provisioning Error Access Denied

Hello,

It’s. my first time to use the momo api. I am trying to create a user in sandbox using firebase authentication trigger function. I subscribed for collections widget and am passing its primary key as the Ocp-Apim-Subscription-Key.

the user is being created successfully when i run in the sandbox but returns access denied when i execute the code.

import * as admin from "firebase-admin";
import * as functions from "firebase-functions";
import { v4 as uuid4 } from "uuid";

export const createUser = functions.auth.user().onCreate(async (user) => {
    const uid: string = user?.uid;
    const myUUID = uuid4();
    const key = functions.config().primarycollection.key;
    console.log(myUUID);
    try {
        await admin.firestore().collection('users').doc().set({
            userId: uid,
            myUUID,
            createdAt: user.metadata.creationTime,
        });

        const provideUser = await fetch("https://sandbox.momodeveloper.mtn.com/v1_0/apiuser", {
            method: "POST",
            body: JSON.stringify(
                {
                    "providerCallbackHost": "momocallback.mtn.com",
                }
            ),
            headers: {
                Accept: "application.json",
                "X-Reference-Id": myUUID.toString(),
                "Content-Type": "application/json",
                "Host": "sandbox.momodeveloper.mtn.com",
                "Ocp-Apim-Subscription-Key": key!,
            },
            cache: 'default'
        });

        if (provideUser.ok) {
            const data = await provideUser.json();
            console.log(data);
        } else {
            console.log('error provisioning user', provideUser.statusText);
        }
    } catch (error) {
        console.log(error);
    }
});