Customer portal add-on not available on Office 365 Admin

Hi everyone:

We are using Dynamics CRM 2016 Online Update 1 with our Internal Use Rights licenses. We plan to provide support services to our customers and would love to do that using the Customer Portal functionality that's available on CRM 2016 Update 1.

Reading this forum and searching the web, I found that the Customer Portal add-on should be bought on the Office 365 Admin portal.

But I can't find it. There's an entry for Employee Self-Service, but no Customer Self Service.

Does anyone know how can we enable it?

Thanks,

Ivan