This AppleScript will toggle the iTunes player on macOS between two states, play and pause. It can be triggered from any application that can trigger AppleScripts.

play-pause-itunes.scpt

try
-- Specify the application will want to work on, in this case iTunes.
	tell application "iTunes"
	        -- Get iTunes current state
		if player state is paused then
		-- If iTunes is paused, press play.
			play
		-- Get iTunes state if it doesn't match the first condition
		else if player state is playing then
		-- If iTunes is playing, press pause.
			pause
		end if
	end tell
end try