Unable to install a SharePoint Add-In in Office 365 Germany

[Anton Khritonenkov]

We created Office 365 Germany subscription and tried to install SharePoint Add-ins from SharePoint store. We were able to in install none of the available add-ins from the store. All of them throw this error:
"Everything is fine, but we had a small problem getting your license. Please go back to the SharePoint store to get this app again and you won't be charged for it."

Our partners submitted a ticket to Microsoft and they replied that software providers have to update Add-Ins for German Cloud. We tried to find any options related to German Cloud in our Microsoft Seller Dashboard, with no luck.

I'm not able to find any guidance on this on the Internet as well. 

All the add-ins from the store throw the same error. This doesn't look like a problem of a software provider. 

So, what are requirements to make SharePoint add-in work in German Cloud (Office 365 German)?

[#2]

Interesting scenario, I don't see how the issue could be related to the fact your tenant is hosted in Germany but it's also true that Office 365 in Germany is being managed by T-Systems...when you call support: did you get support from Microsoft or from T-Systems?

[#3]

It is not regular Office 365 subscription. It is Office 365 Germany. Special version for Germany regulations. https://products.office.com/de-de/office-365-deutschland/compare-plans-pricing#bat2-1?tab=bat2-1. We and our partners created a few subscriptions. The same problem. Our partner submitted a ticket via Central Admin panel. The answer I provided is in the initial question. So, we are trying to understand what "Update add-in for German Cloud" means.