Not sure if there can be a “logic code” where the player can recieved payment via aid once during the duration of the cast only or if successful TS.
Caster casts blessing on a player (duration 12 hours). Within that 12 hours, player can “pay” via aid.
Also, some sort of feature where the caster can cast a TS on “enemy”, at the same time input “for which kingdom” (or select yourself) and enter “gold amount”. The TS would be shown as successful or Unsuccessful, but no details (yet). Once the player send the gold amount, the TS would be revealed to both kingdoms (caster and player). Or the caster can choose to do it for free and select himself.
This way other races can also be Casters and if aid sending is purely for magic, this is a good compromise… I don’t know if this can be easily done.