Here is a summary related to the OpenVPN Connect client used as in Android, Linux and Windows.
This is a free program but was designed to work with the OpenVPN Connect Server software, that you have to pay for.
For some reason OpenVPN decided not to support all the capabilities available in the OpenVPN Community Server in the OpenVPN Connect Server. That includes the options related to OTP and to the use of pkcs12 certificate containers.
They do support OTP but the setup is different to how it works in the OpenVPN Community Server.
Originally, because of demand they did include a temporary hack to work with pkcs12 certificate containers. However later on they decided they would not support those certificate containers and so you have to have the certificates split up into ca, cert and key.
The OpenVPN Community Server software continues to support pkcs12 containers.
(Incidentally, with the CU197 version any new client created has the certs embedded directly in the .ovpn file, although you can still download for the client a pkcs12 container file if required.)
Earlier this year OpenVPN changed their OpenVPN Connect software to flag up that pkcs12 was no longer supported but in the interim would still be accepted.
Now with the latest OpenVPN Connect version it looks like they have moved from still accepting the pkcs12 container to saying that it is unrecognised.
@dark0ipfire and @cordth your error messages are saying that the otp options are allowed with OpenVPN Connect but not at the client end. They can only be used by pushing from the OpenVPN Connect Server software while the OpenVPN Community Server works fine with them at the client end.
The OpenVPN for Android app and Network Manager in Linux both use the OpenVPN Community software for their clients and not the OpenVPN Connect software.
Basically OpenVPN have made their “pay” OpenVPN Connect Server just a bit misaligned with their “open source” OpenVPN Community Server and the Connect client is aligned with the Connect Server.
Basically if you use the Connect client, you will need to modify the client .ovpn to remove any parts from the Community related version that are not compatible with the Connect version or use the OpenVPN for Android version that is matched to the OpenVPN Community Server software. I have been using it for years.