CertPathValidatorException: Trust anchor for certification path not found

If you’ve started to encounter the following exception, especially on older Android devices, this guide can help:

handleFetchPinError: com.android.volley.NoConnectionError: javax.net.ssl.SSLHandshakeException: java.security.cert.CertPathValidatorException: Trust anchor for certification path not found.

then you should ask the backend engineer to give you the a digital certificate of the api url that you want to connect to.

Solution Steps (Backend Server Setup):

if you are using letsencrypt then the file should be located at `/etc/letsencrypt/live` directory. look for the domain name. go to that folder and you will see that there is a file named `fullchain.pem`. copy the entire contents of the file then create a new file with with extension `.crt` and hand it back to the android developers. you can choose any name as you wish. for our case we named it `api.mysite.com.crt`

On the android side:

1. copy the file into `res/raw` folder.
2. create a new folder under `res` folder `xml`. and under it, create a file network_security_config.xml

Here is what the `res/raw/network_security_config.xml` file should look like:

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
 <domain-config>
 <domain includeSubdomains="true">api.mysite.com</domain>
 <trust-anchors>
 <certificates src="@raw/api.mysite.com" />
 </trust-anchors>
 </domain-config>
</network-security-config>

you can also add multiple configuration like above for test or dev servers. (be sure to get two certificates for production and test apis)
here is an example:

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
 <domain-config>
 <domain includeSubdomains="true">api.mysite.com</domain>
 <trust-anchors>
 <certificates src="@raw/production_certificate" />
 </trust-anchors>
 </domain-config>
 <domain-config>
 <domain includeSubdomains="true">devapi.mysite.com</domain>
 <trust-anchors>
 <certificates src="@raw/test_certificate" />
 </trust-anchors>
 </domain-config>
</network-security-config>

3. Specify the network configuration settings in the `AndroidManifest.xml` file of your application.

android:name=".MXVHR"
….
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme"
android:usesCleartextTraffic="true"
android:networkSecurityConfig="@xml/network_security_config" <- Add this line here
tools:replace="android:icon"

This gist has been written with the help from the following link:
https://dev.to/enyason/how-to-fix-issue-of-ssl-handshake-exception-on-android-g6g

Many thanks to the original author: Enya Emmanuel