Certificate not accepted by gpstracker (gpstracker binding)

Hi, I am trying to get the gpstracker-binding to work using gpstracker app on android and openhab by installing Habian on Debian 9 on a laptop. I connect to my laptop with nginx installed. I just did what is in the manual, I do not really understand most of what nginx does, so be gentle!
The url I have set is this:
The port I am using is already working for my sitemap through the openhab app (or is this the cause???)

When I click on ‘Validate certificate’ all seams good. But in the logs I get the message: could not send to url.
certificate not accepted. And when I show the url in the settings and wait for a while, I get an error message that reads ‘certificate not accepted’.
I do not get anything in the openhab-log.
What should I do to get this working?