I have just tried and I can’t reproduce your problem.
I created a new connection called testing with the remark testing and the hostname testing and password testing.
That created with no problem.
I then deleted that connection and re-added the same connection with exactly the same entries for each line and it was created without any problem.
The connection info is stored in
/var/ipfire/ovpn/ovpnconfig
You can check in there to see if the hostname or connection name that you are trying to use is already used by another connection.
Both the connection name and the certificate hostname need to be unique.
If you are getting the openssl 256 error then look in
/var/log/httpd/error_log and it will show more details on the issue that caused the error.
If the error is
A challenge password []:An optional company name []:Cannot write random bytes:
4097A65AC7790000:error:12000079:random number generator:RAND_write_file:Cannot open file:crypto/rand/randfile.c:240:Filename=/var/ipfire/ovpn/ca/.rnd
Then look in this post for the answer.
https://community.ipfire.org/t/openssl-cant-open-var-ipfire-ovpn-ca-rnd/10326/3