SP on bet fair
You don't have a choice. If you choose to take SP then your bets will be matched at SP and that can lower or higher than you anticipate depeding on various factors but mostly to do with back and lay volume that are set at SP.
But if you're asking where is the SP button then you will find at the bottom of the manual bets tab (and most others) in the unmatched section and you can select to take SP if it doesn't get matched to your desired price before going in play.
But if you're asking where is the SP button then you will find at the bottom of the manual bets tab (and most others) in the unmatched section and you can select to take SP if it doesn't get matched to your desired price before going in play.