It generaly depends on the package you installed, but the common way to go is to start by checking the details of the installed Flatpak application (using
grep
can specifically help find an application, if we know it contains a partial string) e.g.
flatpak list | grep viber
(grep is case-sensitive, so try capitalising the "v" in "viber" if no results are initially found to see, if that works). That should give you the application ID (along the lines of
com.developer.application
). Just copy the application ID and enter
flatpak run application id
in the terminal. That will launch the application verbosely and therefore should display any errors.