Why do classmates make a request for payments via https with an error?

Question

Classmates

I changed the address to the payment callback script from http to https, and now the request to the script through the browser and its work are normal, but payment errors come to the soap from classmates (absolutely for every payment attempt, the application balance for today is 0). The error is the same:

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
sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
unable to find valid certification path to requested target

OK does not trust the certificate, or what?

Answer 1

I 'm clarifying anvoevodin 's answer (since I don't have the right to edit someone else's answer)
Most likely there is an untrusted certificate on your server (for example, self-signed). In this case, use the service and create a valid certificate on one of the sites that allow you to do this for free, for example,
https://buy.wosign.com/free/
https://www.startssl.com/
Validate whether your certificate is valid, or we knocked on the hacker machine that we put in front of your server when intercepting traffic, the client in this case cannot and, for security reasons, refuses to connect.