Problem integrating WMS with https-connection

Dear Qfield-experts,

I have a weird behavior in my application:

I try to integrate WMS from https://charta-thesauri.de/cgi-bin/mapserv?map=LKOS

in my application (lets say the layer “Landkreis”).

Without any problem I can integrate this https-WMS-layer e.g. in QGIS, in OpenLayers, in ArcGIS online etc. etc.
But in qfield I get the information, that this layer could not be loaded?

Surprising is:
If I try it without https:

http://charta-thesauri.de/cgi-bin/mapserv?map=LKOS

…it works immediately, also in qfield.

I have bought official SSL-certificates from https://www.sectigo.com.
I have tried it with an official “Business certificate” and also with an “Wildcard certificate”.
But WMS-Layer with these certificates do not work in Qfield.

Do you have an idea, what to do?

Thank you very much, Kai

I changed the SSL-Certificates from sectigo.com to SSL-Certificates from “Let’s Encrypt”. Now it works fine.