HTTP-Binding error receiving from HTTPS

can anyone help me toot ?
Trying to get http-binding from an https server. (This server runs on the same raspberrypi as openhab2):

2017-11-11 21:02:22.778 [ERROR] [org.openhab.io.net.http.HttpUtil ] - Fatal transport 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
2017-11-11 21:02:22.785 [ERROR] [ab.binding.http.internal.HttpBinding] - No response received from ‘https://192.168.1.50/beckhoff/callajax.php

i downloaded local at my browser the cer File and imported it to my java_home keystore, restartet again, but same failure.

wget on rpi shows:
wget https://192.168.1.50
–2017-11-11 21:21:38-- https://192.168.1.50/
Connecting to 192.168.1.50:443… connected.
ERROR: The certificate of ‘192.168.1.50’ is not trusted.
ERROR: The certificate of ‘192.168.1.50’ hasn’t got a known issuer.
The certificate’s owner does not match hostname ‘192.168.1.50’

my item looks like this:
Number Lagerraum_Light_Out “Value: [%.1f ]” { http=“<[https://192.168.1.50/beckhoff/callajax.php{Authorization=Basic xxxxxxxxxxxxxxxxx==}:3000:JSONPATH($.Lagerraum_Light)]” }

please help.
thanks,