How can I use Firebase admin sdk(Verify Token) with Load Balancer

Question

I'm trying to verify the firebase token with Firebase Admin SDK(VerifyIdToken()) to receive uid using NestJS Web Socket. It worked pretty well when the server was single WAS. But after I scaled up the server with Load Balancer it always return this error.

Error

FirebaseAuthError: Error while making request: connect ETIMEDOUT

errorInfo: {
    code: 'auth/argument-error',
    message: 'Error while making request: connect ETIMEDOUT 'IP Address:443.'
}

Servers connected to Load Balancer(I Connected two server) have different IP with exactly same logic. Every server have Firebase Token Verification function.

    //To Verify Firebase Token, return uid
    async VerifyFirebaseToken(Token: string): Promise<string> {
        try {
            const VerifiedToken = await this.firebaseVerifierApp
                .auth()
                .verifyIdToken(Token);
            return VerifiedToken.uid;
        } catch (error) {
            console.log(
                'Critical error occured!! See details below.',
            );
            console.log(error);
            return '';
        }
    }

and how I initialized the firebase app

    this.firebaseVerifierApp = firebase.initializeApp({
        credential: firebase.credential.cert(firebase_params),
    });

I think the problem is, the Load Balancer is not guarantee the firebase Verification callback goes back to where the request sended.(Sended to other server or somewhere else I guess).

How can I guarantee the verification call back goes back to where the request sended? If what I guessed is wrong, is there anyway to fix it?