I have fixed that problem, you need to add a dummy key. The VPN provider doesn't care about it, it will be just used for the encryption tunnel.
Can you provide us a dummy private key?
I googled for some private keys, but whatever private keys I found, the TrueNas-interface keeps telling me that "A valid private key is required, with a passphrase if one has been set."
For example this private key will not be accepted:
(can be found here: https://gist.github.com/renatolfc/f6c9e2a5bd6503005676)
-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----