Checkins are no longer possible, but you can use the "Share" function instead.
After the Cambridge Analytica scandal, Facebook decided to prohibit 3rd party apps to post to user's walls, which was mandatory in case of checkins. Only the user can post to it's on wall.
After 1st of August, 2018 the following will not work at all:
- checkins (you can use the share function instead), as publish_actions is deprecated in Graph API 3.0 and external apps can no longer create a post automatically in the user's name on their timeline
- link to users' profiles (deprecated by Facebook)