How can I add Access Authentification to Nitro Sign?

[STEVEN SCHNUR]

I'm currently on Nitro Productivity Suite  which includes Nitro Pro 13 and Nitro Sign for unlimited eSignatures. I'm seeing that you've now added Access Authentication as an option but it tells me that this is not available on my plan if I try to use it. What do I need to do to add it to my plan or a new plan and what would the cost be? Since I'm required to authenticate signatures already I'm hoping it would save me the confusion of having my clients authenticate via separate emails. I'm the only person in my company so I'm the only one who would be using this service. Thanks.