iReceivables External user self registration

Hello,

Need suggestions oniReceivables External user self registration..

We are implementing Oracle iReceivables and had some doubts related to External user registration.

 

How to enroll an external customer in iReceivables? We have around500K + customers, and it will not be easy to enroll every individual
customer by creating user (fnd_user) and configuring self-service roles.

 

Is there any functionality in iReceivables where we can send self-registration to the customers via email and they can dothe self-registration? Or any other approach? Will system itself identify  
customer contact by itself to send an self-registration link/email?

 

Also when an external user tries to create a self-registration, they cannot or should not add any othe rcustomer account, is there any validation that will trigger an approval process