webmention.rocks fails 22 of 23 tests

[Libralop]

Today I tried webmention.rocks to test my kirby site (https://libralop.de/tagebuch/2016-12-16) with your webmentions plugin.

Problem: 22 of the 23 tests failed (see appendix pings.json.txt). Only test 15 worked.

I installed and set up the plugin as described in the manual. Receiving webmentions via bridgy works fine. What do I have to do to make the sending of webmentions work?

BTW: Is there a way to support your development work for this plugin?