To grant free access to certain clients, yet keep ‘Require Purchase’ on for the general public, you will need to manually add these members to the product that gives access to the Premium content when purchased.
To do this:
On the lefthand black sidebar, navigate to Sell > Products.
Click on the product that gives access to the Premium content you want to grant free access to.
For existing members, Click the ‘Add Member’ button, then hit the small ‘+Add’ button to the right of their name in the popup window. They should now have access to this premium content without having to purchase it. You can send them an email notification by clicking 'Share' > 'Assign to a member' then assigning the member and clicking the 'Notify' button next to their name (on the page containing the particular product you've given them access to).
If the client is new to your app, select 'Create Member' from the 'Add Member' area, enter their email and name, then add them to the product.
Copy the link to the page the content is on and send it directly to your client over email, text, social media or whatever else you like. Be sure to tell them to sign up with the same email you added them as a member with.
Once they sign up, they should have access to this premium content without having to purchase it.