Client issued T4A - box 20 to message therapist, should it be box 48. Client pays a percentage of the service fee to message therapist.
More correctly, around here, it should generally be on the T4.
However, Massage therapists popular folk lore is to usually just do it their own way.
Perhaps the massage business could invite a CRA Liaison Officer in for free help in evaluating their business structure.
(Liaison Officer service - Canada.ca)
Probably the box 48 is more correct, that is how I see it reported for my own RMT client. You may just need to manually post to the correct line on T2125?