How to bet at sp

Hi, I would like to place a lay bet at the starting price.
Do I just use actual_sp in the price section of the trigger? Would I need to set the trigger time to fire off at a particular time as well? What about the market status?

Hello!

To bet at SP, just choose "back at SP" or "lay at SP" as the trigger action, the specify the price limit (or put 0) and the liability.