server certificate verification failed

Hello,
I'm Francesco from Bticino.
We are trying the Stash product with an evaluation license in order to decide if adpot it or not in our company.
I've installed stash without any problem and I've also put it on https with success.
But now I get an error when trying to clone a git repository by using https protocol (ssh works fine). When I run "git clone" command on my client the system return to me this error:server certificate verification failed
"
> git clone https://stashadmin@<myurl>:8443/scm/myh/myhomeinternational.git
Cloning into 'myhomeinternational'...
fatal: unable to access 'https://stashadmin@<nyurl>:8443/scm/myh/myhomeinternational.git/': server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none
"
I'm sure I'm doing something wrong, but I don't know what!
Please. Can you help me to fix this error?

Thanks in advance.

Francesco