No entries in Amazon App Store on new (refurbished) Fire phone

I got a refurbished Fire phone. When accessing the Amazon App Store, I get an empty page. Searching the App Store delivers zero results for every query. Looking at the Amazon App Store on the web shows that the Fire phone cannot be selected as a device. On the internet, I cannot find any information that Amazon has stopped to support the discontinued Fire phone in the App Store. How can I fix this issue?