How to keep the user logged in using Google client side javascript API with updated Google API

I am trying to implement google sign-in. I did, however the user is logging out after refresh action.

I have recently migrated to google's updated javascript client-side script API.

The code is live at Expense by Cutezero. I have used the below code to enable sign in

if (gapiInited && gisInited) {
        tokenClient.callback = async (resp) => {
            if (resp.error !== undefined) {
                throw (resp);
            }
            // await listLabels();
            await listFiles();
        };

        if (gapi.client.getToken() === null) {
            // Prompt the user to select an Google Account and asked for consent to share their data
            // when establishing a new session.
            tokenClient.requestAccessToken({ prompt: 'consent' });
        } else {
            // Skip display of account chooser and consent dialog for an existing session.
            tokenClient.requestAccessToken({ prompt: '' });
        }
    }

Please request more info in case you need it. But you can refer to the live-site to get more details.