Thank for trying to help.
As described the problem was a missing ssl certificate named cafile.
A quick fix is to switch off the ‘ssl’.
A better solution is to define in your php.ini the openssl.cafile variable
If I’m right grav brings already such a certificate.
It can be found under /vendor/composer/ca-bundle/res/cacert.pem
More ideas can be found under:
greeting
Thoomyy