I wanted to try this myself, but I ran into two problems right away trying to follow your instructions. First, your step 1 that says "open pega express". I thought that meant go to developer portal and click " [ cube ] > new application > express application". But apparently it doesn't. It seems to mean go to developer portal to lower left (I had to decrease my chrome zoom to even see the lower left!) and click the two little arrows that point to each other.
The second problem was that when I got to your step that said click "send invitation", although I didn't see any errors, nothing arrived in my email, so there must be some basic email setup I need to do on the pega side to make this all fly.
If you tell me an easy way to get past that, I'll be happy to try again.
Snagged on that default email thing. I just went to designer studio > integration > email > outbound email > default, and it says something like outlook.office365.com . I clicked "test connectivity" and everything says "success". But when I try your "send invitation" step, I get nothing. I tried both my pega (business) email address and my rcn (home) email address as the target. /Eric