Authy VPN has a lot of debug logs to help you diagnose issues. Start by editing your vpn server.conf so that it creates a log file.
Add the following lines at the end of: /etc/openvpn/server.conf
status openvpn-status.log
log openvpn.log
log-append openvpn.log
verb 4
If the pluging is loaded correctly, it will log this line at initialization:
sudo cat openvpn.log | grep '\[Authy\]'
[Authy] Authy Two-Factor Authentication started
Authy will also log all the authentication activity on openvpn.log
[Authy] Authy Two-Factor Authentication started
[Authy] Authenticating: [email protected], token=1234567 and AUTHY_ID=1
* About to connect() to api.authy.com port 443 (#0)
* Trying 107.23.117.172...
* Connected to api.authy.com (107.23.117.172) port 443 (#0)
* successfully set certificate verify locations:
* CAfile: none
CApath: /etc/ssl/certs
* SSL connection using ECDHE-RSA-AES256-SHA
* Server certificate:
* subject: serialNumber=STgISFc5XC8h7Ocjt9n9-dNQ/cxTm75c; OU=GT76495531; OU=See www.rapidssl.com/resources/cps (c)12; OU=Domain Control Validated - RapidSSL(R); CN=api.authy.com
* start date: 2012-12-16 08:56:17 GMT
* expire date: 2014-01-18 09:08:03 GMT
* subjectAltName: api.authy.com matched
* issuer: C=US; O=GeoTrust, Inc.; CN=RapidSSL CA
* SSL certificate verify ok.
> GET /protected/json/verify/1234567/1?api_key=004436f9c97c9988253bd95933296580 HTTP/1.1
Host: api.authy.com
Accept: */*
< HTTP/1.1 401 Unauthorized
< Server: nginx/1.1.19
< Date: Fri, 16 Aug 2013 20:14:00 GMT
< Content-Type: application/json;charset=utf-8
< Content-Length: 88
< Connection: keep-alive
< Status: 401 Unauthorized
< WWW-Authenticate: Basic realm="Access Denied"
<
* Connection #0 to host api.authy.com left intact
[Authy] Curl response: Code=0, Body={"success":"false","message":"token is invalid","errors":{"message":"token is invalid"}}
[Authy] Auth failed for [email protected]