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The first thing I would suggest is to log out of your iTunes Store account on your iPhone.
Then restart the device and log in again.
If the above did not resolve your issue, follow the troubleshooting steps in the article below.
The link includes the complete details and screenshots, but I've highlighted a few points for you:
- Make sure that your iOS software is up to date by connecting your iOS device to iTunes and clicking on Check for Update in your device's Summary page in iTunes.
- Check and verify that you are in range of a Wi-Fi router or base station. If you are on a 3G capable device, make sure that cellular data is turned on from Settings > General > Cellular.
- Check to make sure you have an active internet connection. You can check the User Guide for your device for help with connecting to the internet.
- Check to make sure other devices (portable computers, for example) are able to connect to the Wi-Fi network and access the internet.
- Try resetting (turning off and then on again) your Wi-Fi router
- If the issue still persists see, iOS: Troubleshooting Wi-Fi networks and connectionsoriOS: Troubleshooting Wi-Fi networks and connections.
I hope this information helps ....
Have a great day!