EnvelopeGenerator/EnvelopeGenerator.Web/MessageKey.cs

namespace EnvelopeGenerator.Web
{
    public enum MessageKey
    {
        ServiceOutputNullError,
        UnexpectedError,
        FailedToSendAccessCode,
        WrongEnvelopeReceiverId, //the value should be about URL (like URL is not existing) as a part of security.
        DataIntegrityError,
        NonDecodableEnvelopeReceiverId
    }
}