I created a .desktop file for an #app that comes as an executable binary (without an icon) and added a custom icon to it.
In the #gnome app grid, both the app and my #icon show up as desired, but not in the #dock, where the generic executable binary icon still shows up.
Do I need to clear some kind of cache to make this work?
PD: Rebooting did not help and some commands (e.g. ’update-icon-caches /usr/share/icons/*’) shared around the internet didn't either. 
@amadeus the application must either use a Wayland app id or an X11 WM_CLASS that matches the name of the desktop file minus the extension, for GNOME to match its windows to the desktop file and use the icon
@ebassi Thank you for your help! Turns out I already did everything right. Today, when I went to double check everything, it suddenly worked as expected. 