Hello, 

I'm having the same issue. How can we resolve this?

Regards,
Daniel 

I was able to get our existing box.com users added to the enterprise by turning off the New Look option. While it was on, I was unable to send the invite to them. Once it was turned off, the invite option became available to me when adding them.

Thanks Kylee, how do I turn off the 'New Look' option?

597261538 if you go into the admin console > Users & Groups > on the upper right corner of the page, above the "Add Users" button there should be a button that says "Leave New Design". Once that is toggled off, you should be able to send the invite.