SSL issue with Apple pay web integration

I am seeking an assistance with an issue we've encountered during our efforts to integrate Apple Pay into our web application. We're using Angular on our client side. and our server side is powered by AEM(Adobe Experience Manager), which is based on Java.

As part of our integration process, we're following the Apple Pay documentation. However, we've encountered a challenge during the merchant validation step. Our server-side implementation, responsible for validating the merchant identity and generating a session object for payment requests, is encountering an SSL handshake error.

Here's the error message we're encountering:

javax.net.ssl|FINE|01|main|2024-03-20 05:19:52.812 IST|SSLCipher.java:1817|KeyLimit read side: algorithm = AES/GCM/NOPADDING:KEYUPDATE countdown value = 137438953472 javax.net.ssl|FINE|01|main|2024-03-20 05:19:52.813 IST|SSLCipher.java:1971|KeyLimit write side: algorithm = AES/GCM/NOPADDING:KEYUPDATE countdown value = 137438953472 javax.net.ssl|FINE|01|main|2024-03-20 05:19:52.849 IST|SSLCipher.java:1817|KeyLimit read side: algorithm = AES/GCM/NOPADDING:KEYUPDATE countdown value = 137438953472 javax.net.ssl|FINE|01|main|2024-03-20 05:19:52.850 IST|SSLCipher.java:1971|KeyLimit write side: algorithm = AES/GCM/NOPADDING:KEYUPDATE countdown value = 137438953472 javax.net.ssl|FINE|01|main|2024-03-20 05:19:54.082 IST|Utilities.java:73|the previous server name in SNI (type=host_name (0), value=apple-pay-gateway-cert.apple.com) was replaced with (type=host_name (0), value=apple-pay-gateway-cert.apple.com) javax.net.ssl|FINE|01|main|2024-03-20 05:19:54.448 IST|SSLCipher.java:1817|KeyLimit read side: algorithm = AES/GCM/NOPADDING:KEYUPDATE countdown value = 137438953472 javax.net.ssl|FINE|01|main|2024-03-20 05:19:54.448 IST|SSLCipher.java:1971|KeyLimit write side: algorithm = AES/GCM/NOPADDING:KEYUPDATE countdown value = 137438953472 javax.net.ssl|SEVERE|01|main|2024-03-20 05:19:54.453 IST|TransportContext.java:369|Fatal (CERTIFICATE_UNKNOWN): sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target ( "throwable" : { sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:439) at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:306) at sun.security.validator.Validator.validate(Validator.java:271) at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:312) at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:221) at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:128) at sun.security.ssl.CertificateMessage$T13CertificateConsumer.checkServerCerts(CertificateMessage.java:1339) at sun.security.ssl.CertificateMessage$T13CertificateConsumer.onConsumeCertificate(CertificateMessage.java:1230) at sun.security.ssl.CertificateMessage$T13CertificateConsumer.consume(CertificateMessage.java:1173) at sun.security.ssl.SSLHandshake.consume(SSLHandshake.java:376) at sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:479) at sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:457) at sun.security.ssl.TransportContext.dispatch(TransportContext.java:200) at sun.security.ssl.SSLTransport.decode(SSLTransport.java:155)

    at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:280)
    at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:434)
    ... 24 more}

}

We've reviewed our server configuration and checked that the SSL/TLS settings are correctly configured. Additionally, we've ensured that the server's SSL certificate is valid and up-to-date.