The certificate is not signed by a trusted authority (checking against Mozilla’s root store). If you bought the certificate from a trusted authority, you probably just need to install one or more Intermediate certificates. Contact your certificate provider for assistance doing this for your server platform.
I am assuming you do not have the root CA in your Cert Store as trusted. Check your trusted Root CA store and make sure it has “DST Root CA X3”. I am not sure what platform you are on, so I cannot explain how to check this.
Thank you so much for the quick feedback @yrootberg
I am not technical at all (yet). Nevertheless i am using hosteurope. They have an interface where you can upload cert and key as well as uplaoding a “CA file”. I guess thats the missing part. Any idea where i can download the intermediary certificiate file. I tried googeling it and just found this: https://www.identrust.com/certificates/trustid/root-download-x3.html
I would also like to mention that whatever method you used to get the certificate probably should offer you some way to get the intermediate cert (which is most likely what the hosting provider refers to as the CA file). Although downloading it from Let’s Encrypt’s site will work fine, it should not be necessary.
This is a good thing to keep in mind for the long term. Some day Let’s Encrypt certificates may be issued under a different intermediate CA, so in the long term, like some years from now, you shouldn’t assume that the CA file will always be the Let’s Encrypt Authority X3 certificate that it currently is.
