I have created Open VPN via webUI with HMAC key and CRT file.
I developed .NET app and was able to read OpenVPN profile via web API calls, but CA and HMAC fields are empty. I can read only paths (in etc/vuci_uploads/…).
Can you try this command /api/certificates/config to download all certificates, keys, DH parameters, and CA? More information in this link: Teltonika Networks Web API