You need to specify both the certificate you want to revoke, and the account or private domain key which was used to sign / obtain the original key.
Note: the key used needs to be an RSA key currently ( EC keys are not supported for revoking a certificate yet), so you will need to use the RSA account key to revoke a cert signed with an EC domain key.
## Issues / problems / help
If you have any issues, please log them at https://github.com/srvrco/getssl/issues