Enable External Sharing
The External Sharing feature enables your users to share a specific form with external users (those with no access to your SharePoint environment). These external users will be able to view and edit the form and participate in any workflow you have defined.
External Sharing is ideal for scenarios where you need to involve external people in populating data in your forms without giving them any access to your Office 365 / SharePoint Online environment. Things like gathering feedback and collecting signatures are now super easy to accomplish.
Enables email notifications for the external users if they are granted access to a specific form by an internal user. The notification can contain a link to the form to enable them to edit it after they request a temporary PIN. The system will email them the PIN and once they enter it they can open the form.