How to fix "Cannot connect to iTunes Store"

Additional notes:

I have done these steps(If you can’t connect to the iTunes Store - Apple Support) , all are ok.

Fix the issue on your iPhone, iPad, or iPod touch

If you can't connect to the iTunes Store on your iPhone, iPad, or iPod touch, make sure:

1. That your date, time, and time zone are correct. Tap Settings > General > Date & Time. Time Zone might list another city in your time zone.
2. That your iOS software is up to date. To check for updates, tap Settings > General > Software Update. You can also connect your iPhone, iPad, or iPod touch to iTunes and click Check for Updateon your device's Summary page.
3. To check that you're in range of a Wi-Fi router or base station. If you're using cellular service, make sure that cellular data is turned on from Settings > Cellular. If you're connected to cellular data, larger items might not download. You might need to connect to Wi-Fi to download apps, videos, and podcasts.
4. That you have an active Internet connection. For help with your connection, check your device's user guide.
5. To see if other devices, like portable computers, can connect to the Wi-Fi network and access the Internet.
6. To reset your Wi-Fi router by turning it off and then on again.

iOS, I'm using iPhone 7

App store is working fine.

I can open, search, and install, but when i tap "Buy" it shows just like my screenshot.