I can't redownload the Pinterest app

Try resetting the App Store:

Close the App Store completely from the app switcher window by double clicking the Home button and swiping up the App Store preview pane until it disappears from the screen. Then sign out of the iTunes Store (in Settings).

Then do a forced restart. Hold down the Home and Wake/Sleep buttons at the same time for about 15-20 seconds until the Apple logo appears.

Then sign back into the iTunes Store and try downloading again.

Also check Settings > General > Restrictions > and make sure that the iTunes Store, Installing Apps, Deleting Apps, and In-App Purchases are all under the Allow section.

All I can suggest is trying the download through iTunes or contacting Pinterest to see if they can help.

https://help.pinterest.com/en/articles/quick-fixes-common-problems#Web