Some weeks ago I searched and requested an app here .
The message I got (and I still get) is:
"Application eus.euskotren.app was NOT FOUND 
But it is now suggested!
Note: This app already exists"
So it says that the app already exists (in the app store, I presume), but when I look it up it’s not there. What else could I do for the app to be included in the app store? Thanks.
That is one of the issues we have with the App Installer …it does not give a proper explanation as to why the app is not showing in the repository and what the user needs to do to get it there in such cases.
There are a number of these issues already noted here. Will update once the fixes are in place.
If it is an important app for now as a workaround you can download it from FDroid or Aurora Store.