enterprise app Unable to Verify iPhone Distribution

"Unable to Verify iPhone Distribution: My Distribution certificate" Apps. A network connection is required to verify "iPhone Distribution: My Distribution certificate" apps on this iPad. Connect to the Internet and try again".

But everything is OK with my internet connection. I found even here: https://support.apple.com/en-gb/HT204460 that there is a service ppq.apple.com, that verifies enterprise apps, but this service is unavailable on link: https://ppq.apple.com , return error 503.

Whats happened and how can i fix this issue?
And how periodically does the Apple device checks the verification status of the distribution certificates of my app?
Am i alone face this issue?