Good morning @Ionel Dorel 

Which app exactly do you mean? And which app store?

I have a subscription to o2 and I don't know how to find out details about the internet, I can't download the application on ios

tells me the app is invalid

You did look for the “Mein o2”-App, yes?

yes i searched and it is not valid give me app moje O2 something czech

Where are you located, @Ionel Dorel ?

In Germany

Hello @Ionel Dorel,

thank you for your enquiry with us in the community.

And thank you for your help with this request @SethVanDoom

Have you tried changing the region of your app store? Apple has instructions on how to do this:

• Open the Settings app.
• Tap your name and then tap Media & Purchases.
• Tap "View Account". You may be asked to sign in.
• Tap "Country/Region".
• Tap on "Change country or region".
• Tap on your new country or region and then read the terms of use.
• Tap "Accept" in the top right corner and then tap "Accept" again to confirm.
• Select a payment method and enter your new payment details and billing address. Then tap on "Continue". You must enter a valid payment method for the new country or region.

https://support.apple.com/de-de/HT201389

Kind regards
Jessica