Hi Zou

Yes the P12 file is exported from OPNSense along with open config and tls key file
Do you have a sample what they looks like ?
What kind of format is needed for CA cert and client cert ?
It would be really helpful if you make an insturction here.

I try use

openssl pkcs12 -in OpenVpn.p12 -out open.crt -nodes

to generate the certs in PEM format.
It follows the structure of

Bag Attributes
    localKeyID: C7 1D 05 DA 0E 3C 5A 06 BF 47 D2 9F E6

-----BEGIN CERTIFICATE-----

-----END CERTIFICATE-----
Bag Attributes: <No Attributes>

-----BEGIN CERTIFICATE-----

-----END CERTIFICATE-----
Bag Attributes
    localKeyID: C7 1D 05 DA 0E 3C 5A 06 BF 47 D2 9F E6
Key Attributes: <No Attributes>
-----BEGIN PRIVATE KEY-----

-----END PRIVATE KEY-----

Also in ovpn file I have changed from pkcs12 OpenVpn.p12 to pem open.crt

and this the error log:

Sat Jan 14 12:52:23 2023 daemon.notice netifd: Interface ‘ovpnclient’ is setting up now
Sat Jan 14 12:52:23 2023 daemon.err ovpnclient[5782]: Options error: Unrecognized option or missing or extra parameter(s) in /tmp/ovpnclient/ovpnclient:12: pem (2.5.3)
Sat Jan 14 12:52:23 2023 daemon.warn ovpnclient[5782]: Use --help for more information.

Thanks,
Rick