Various sources on-line say to check your date and time to make sure it is accurate. Mine was.
Others said to reboot your device. I did with no noticeable impact.
Yet others said to re-synch with iTunes. I don’t like iTunes. I don’t use iTunes. I don’t have iTunes. I don’t even have a machine that can run iTunes. I rely on my kids’ Macbooks if I absolutely need to do something with iTunes, otherwise I avoid it like the plague.
The solution was to log out of the app store. It took me a while to find that option at the bottom of the main App Store page. I logged out. I logged in. Now I could click through to the install page.
Hope this helps!