We have a virtual pfSense. All devices need a certificate to communicate with ouer central proxy infrastructure. Also the pfSense need a certificate. But how can i install a new Root certificate onto the pfSense?

command line "pkg update" error:

Updating pfSense repository catalogue...
pkg: Repository pfSense load error: access repo file(/var/db/pkg/repo-pfSense.sqlite) failed: No such file or directory
Certificate verification failed for /OU=Domain Control Validated/OU=PositiveSSL Wildcard/CN=files00.netgate.com
34405284920:error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed:/build/ce-crossbuild-244/pfSense/tmp/FreeBSD-src/crypto

Can please someone help me?
thanks, tschuegy