Facebook requires that you have the Leads Access permission for the Facebook Business Pages your ads are connected to. While the Leads Access permission is typically enabled for Page Admins by default, there are some cases where the Leads Access permission needs to be enabled separately.
How to see if you have the Leads Access permission
If you are using Business Manager, you can check on which Facebook Pages you are Admin by following these steps:
Access your Business Manager Account
Go to Business Settings
Select Integrations, then select Leads Access in the side menu
Select the Business Page name
Select the People tab to the right
A list of all the people with the Leads Access permission for that Business Page will appear there. If you do not see you name listed, the page owner for that Business Page will need to grant you Leads Access.
Read more about Accessing Leads Data here and another helpful Facebook article on, How to Enable Leads Access Manager