you would need to upgrade java to at least 1.8.0_201. All versions of Java prior to that version will show message “PKIX path building failed”. Alternatively, you can try the approach described here: https://stackoverflow.com/a/36427118/544904
Hey Mark, thank you for your help. Does it mean that you changed server certificate for endpoint api.backendless.com ? Your hint helped me and my service is running again. Thank you.