[Bug]: Unable to install *App*

[kenshanta]

Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a bug that matches the one I want to file, without success.
• If this is an issue with a particular app, I have tried filing it in the appropriate issue tracker for the app (e.g. under https://github.com/flathub/) and determined that it is an issue with Flatpak itself.
• This issue is not a report of a security vulnerability (see here if you need to report a security issue).

Flatpak version

1.15.6

What Linux distribution are you using?

Fedora Linux

Linux distribution version

39

What architecture are you using?

x86_64

How to reproduce

1. Update an old version of Linux Fedora to version 39
2. Kernel update from the Software App Store
3. Updating the Software App Store from the Software App Store
4. Reboot
5. Install any package using the FlatPak (Tried installing Spotify and VsCode)
6. Error Pop-up for both apps at the end of installation

Error Message:
Error pulling from repo: GPG verification enabled, but no signatures found (use gpg-verify=false in remote config to disable)

Luckily the issue was solved by running - in the root directory - the following command:
flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo

source: wxFormBuilder/wxFormBuilder#354 (comment)

Expected Behavior

Successful Installment of an application using the FlatPak distribution

Actual Behavior

Failure to install and popup Errors.
On the other hand, up to my knowledge and research; this issue is prevalent since Fedora Linux v27

Something to consider

Additional Information

IMPORTANT:

The specified version of FlatPak is after the update as I did not know how to roll back to the previous version