I am building a project using next js and firebase. I use the API routes that next offers for signup and login. The code registers the users in firebase but I keep getting this warning: API resolved without sending a response for /api/auth/signup, this may result in stalled requests. This is the code in my /api/auth/signup/. Hopefully, you can help me fix it.

export default function signup(req, res){
if(req.method === 'POST'){
    const {body: {email, password, displayName}} = req;
    createUserWithEmailAndPassword(auth, email, password)
    .then((userCredential) => {
        updateProfile(userCredential.user, {displayName: displayName})
        const {uid, email, phoneNumber, photoURL} = userCredential.user;
        addDoc(collection(db, "users"), {
            id: uid,
            displayName: displayName,
            email: email,
            phoneNumber: phoneNumber,
            photoURL: photoURL,
        });
        res.json(userCredential.user)
    })
    .catch((err) => {
        console.log(err.code);
        console.log(err.message);
    });

} else {res.json({"error": "Route only available for POST method"})}

}