That is a deep level of sub-domain.
Is it added as a A or a CNAME record to the domain DNS at Cloudflare dashboard?
Moreover, to use a
beta.app.chatwindapp.com SSL certificate, I am afraid you would need to purchase Cloudflare Dedicated SSL with Custom Hostname for $10/month. Moreover, you need this since Cloudflare Universal SSL only provide for
More about dedicated SSL certificates here:
Nevertheless, if this error appears in your browser this is a strong indicator that the hostname is not present on the SSL certificate located at Cloudflare edge.
If you require mutli-level sub-domain support you will either need to purchase this feature or upgrade your Plan to Business so that you can upload a Custom Certificate (hopefully if you have one at your host/origin which already supports beta.app.chatwindapp.com.