Is it bogus? “Facebook Business: try Facebook Ads with a free credit”

When I got an email for $15 credit. I decided to give it a try and boost a post on my Page for free.

After Ad customizing and entering my card information which was required in order to claim credit. It just conventionally failed to claim $15 credit at the end.

Now I am constantly getting the email to "Finish boosting your post ...". While opening Ad (draft) it shows no sign of free credit. However, FB successfully ends up with my card information.