User Vivek Gite shows us how to fix a wget cannot verify certificate issue when using Let’s Encrypt with FreeBSD. Let’s Encrypt is an open source certificate authority application. See the link below for the full set of instructions.

I installed GNU wget utility on FreeBSD as explained here. However, whenever I use the wget command to download stuff from the Internet, it says:
ERROR: cannot verify download.freebsd.org’s certificate, issued by ‘CN=Let\’s Encrypt Authority X3,O=Let\’s Encrypt,C=US’:
Unable to locally verify the issuer’s authority.

How do I fix this problem on FreeBSD 12?

Introduction – The default wget settings is to verify the server’s certificate against the recognized certificate authorities. This error indicates that wget is unable to find root certificates locally. You must install root certificates on your FreeBSD server.  ….

Full tutorial: https://www.cyberciti.biz/faq/freebsd-wget-cannot-verify-certificate-issued-by-lets-encrypt/