ERR_CERT_AUTHORITY_INVALID on Android
Why it happens on Android
Older Android versions ship an outdated root store and fail on chains that modern desktop browsers accept.
The fix on Android
Reissue the certificate with a chain that terminates at a root present in older Android trust stores, and confirm the server sends every intermediate. Updating the device is the only other fix.
Is ERR_CERT_AUTHORITY_INVALID happening on your domain?
An external SSL check builds the chain from scratch with no local trust store shortcuts, so it shows a missing intermediate that your own browser may be silently caching around.
Free, no signup. Runs from outside your network, which is the only way to tell a server fault from a local one.
If that didn't fix it
Android has its own failure mode, but ERR_CERT_AUTHORITY_INVALID has a wider set of causes that apply everywhere. The most common one overall is: the server serves only the leaf certificate and omits the intermediate bundle.
All causes and fixes for ERR_CERT_AUTHORITY_INVALID