Advanced option WP-Invoice custom field may be used for adding custom user data fields for payments forms.
For your notifications on any of these Trigger actions — WPI: Invoice Paid (Client Receipt), WPI: Invoice Paid (Notify Administrator), WPI: Invoice Paid (Notify Creator) — you can use these shortcodes:
When a customer pays an invoice using WP-Invoice a user account is create for them. The user information is stored in what's called "User Meta". Other plugins, including WP-CRM, can use this user meta as well.
To have the WP-Invoice's user meta be accessible in WP-CRM you will need to add the fields you are interested in on the CRM -> Settings -> Data page. Below is list of WP-Invoice fileds:
Note! Slug of attributes should be as provided below. You will have ability to change titles after attributes will be saved.