We are using a third party payment service for our web users to be able to pay for courses. Once payment is completed however, payu attempts to connect to our site and run an IPN. However, they get the following error:
javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
Since our certificates are completely correct and up to scratch I can only imagine their services need to have the root CA certificate installed in their java trustore. Is this correct? Or is there something else we are missing?