When entering commands swaymsg gaps inner 10, swaymsg gaps outer 10 nothing happens. Tried to add these lines in .config/sway/config
gaps inner|outer|horizontal|vertical|top|right|bottom|left <px>
gaps outer all set 20
gaps inner all set 20
After reloading config and/or exiting sway session I have this:

The syntax inside the config file is much simpler than the swaymsg syntax. (There is no all since it will apply to all future workspaces and there is no set either.) This works in my config file: gaps inner 8.
Also worth mentioning since I had similar issue just a day ago..
The new gap settings apply only to new workspaces. existing gaps are not retroactively updated.
So in order to get any kind of visual confirmation you need to reload your sway-conf and move your windows to an uninhabited workspace. (or reboot/log out)
gaps inner|outer|horizontal|vertical|top|right|bottom|left <px> changes the default gaps for future workspaces. This can be used in the config file or at runtime, but will not effect existing workspaces
gaps inner|outer|horizontal|vertical|top|right|bottom|left all|current set|plus|minus <px> changes the gaps for existing workspaces, but will not effect future workspaces. Since this affects existing workspaces, it can only be used at runtime
This works in my config file:
gaps inner 8.
Thanks a lot, it helped me.It's kinda funny that the solution was so simple. Loving sway so far
Thank you so much for your help <3
Most helpful comment
Also worth mentioning since I had similar issue just a day ago..
The new gap settings apply only to new workspaces. existing gaps are not retroactively updated.
So in order to get any kind of visual confirmation you need to reload your sway-conf and move your windows to an uninhabited workspace. (or reboot/log out)