FreeBSD 12.1 pkg error: no trusted fingerprints

I have just installed FreeBSD 12.1 and want to give it a try. I used qemu. When I types pkg, it started normal bootstrapping. After downloading, it says No trusted fingerprint found matching package's certificate. I am confused because there isn't any error _**during**_ the installation process. Any ideas? If needed, I will post the log. At the time of 2020/01/04 10:19:45, I reopened this question. Now I have seen this question and this . None of them can help me. I tried by building pkg in port: /usr/ports/ports-mgmt/pkg, but it couldn't build. Gives error: : jemalloc_arena.c:647: Failed assertion: "nstime_compare(&decay->epoch, &time) <= 0