If you are running into this problem, it will be because Android Studio has this quirk where the constraint folder is not in the android directory structure but outside it.
Let’s start from the beginning. The libraries are all in the /User/<username>/Library/Android/sdk/extras/android/m2repository/com/android/support/
However, constraint sits in a slightly different place. It is at /User/<username>/Library/Android/sdk/extras/m2repository/com/android/support/
Note the lack of the android directory.
One work around it is to copy the files from outside the android folder into the android folder structure.
Very weird.