Is found the pre defined action commands action:pause, action:resume ...but i miss action:print (or action:start_print
Sure the question is: For what you need a gcode command to start the current loaded file. Makes on the first look no sense.
I installed a LCD controller BOX and my target was to start also the current loaded file. What i have done is to create a bash script with the api request linked to a custom action command but would be nice if maybe in a future version of Octoprint a predefinded command is available to start a print.