Janrain Engage w Paypal as provider: what is the openid.realm URL ?

[Toad]

Trying to get Janrain engage set up with Paypal as an identity
provider.

Walking through the instructions at
https://openid.paypal-ids.com/rpintro.html

I got as far as
Enter the openid.realm URL: (supply URL)

What do I have to enter for that value into my x.com application
setup ?
I cannot find any docs for that here, at janrain or via google.

Is it something like the other endpoints, ie
http://mycompany.rpxnow.com/paypal/callback

???

[Duke]

Enter your Application Domain from the main application page on rpxnow.com(e.g. 
https://zzzzz.rpxnow.com/).