Our website using Let's Encrypt through Nginx is all green on SSLLabs test (A- score).
But on one Android phone it accepts the certificate and sees the trust chain up to the root certifying authority, but still says the site isn't fully trusted:
here's the certificate info:
How do we fix this?
Partial quote of the text in the first image:
The identity of this website has not been verified. The identity of the server to which you are connected cannot be fully validated. You are connected to a server using a name valid only within your network, and an external certificate authority has no way to validate ownership.
Browser is Samsung 'Internet' version 3.5.38