Yes , the shooter can, but sometimes MDs need to add the person to hold their spot and the person pays later online using their management link. For instance, the two I need to add are in the military and indisposed at the moment but will be back in time the match.
The work around is all well and good unless you're just adding them to hold their spot but you still need the shooter to pay online. Yes, this error is happening to me currently. I have 2 I need to add but will need to pay.