Google One Tap stores user status in the g_state cookie. By default, the
cookie domain is set to the domain of current page.
If One Tap is displayed on the parent domain and subdomains, the state cookie must be visible across all of your domains. In this case, you need to set the cookie domain to your parent domain, mainly when you set the cookie from a subdomain.
You can use the data-state_cookie_domain configuration parameter to change the
state cookie domain. The following code example shows how to set the
data-state_cookie_domain parameter:
<div id="g_id_onload"
data-client_id="YOUR_CLIENT_ID"
data-auto_select="true"
data-state_cookie_domain="parentdomain.com"
data-login_uri="https://login.parentdomain.com/your_login_endpoint">
</div>