According to the current rules, you can use it on the shoulder as an aid to go forward, but NOT as a reprimand (after a refusal, etc.) So maybe that was the confusion?
EV 112 WHIP. The use of the whip must be for a good reason, at an appropriate time, in the right place, and with appropriate severity.
a. Reason: The whip must only be used as an aid to encourage the Horse forward, or as a reprimand. It must never be used to vent an Athlete’s temper. Such use is always excessive.
b. Time: As an aid, the only appropriate time is when a Horse is reluctant to go forward under normal aids of the seat and legs. As a reprimand, the only appropriate time is immediately after a Horse has been disobedient, e.g., napping or refusing. Instances of inappropriate use of the whip include the whip used after Elimination, after the last fence on course, and/or multiple times between Obstacles
c. Place: As an aid to go forward, the whip may be used down the shoulder or behind the Athlete’s leg. As a reprimand, it must only be used behind the Athlete’s leg. It must never be used overhand (e.g., a whip in the right hand being used on the left flank). The use of a whip on a Horse’s head, neck, etc., is always excessive use.