Hydroxycinnamoyl transferase that catalyzes the transfer of an acyl from benzoyl-CoA to tryptamine, to produce benzoyl tryptamine. Serotonin and tyramine serve as acyl acceptors in vitro. Specific for benzoyl-CoA as acyl donor. Has no activity with p-coumaroyl-CoA, caffeoyl-CoA, or feruloyl-CoA as acyl donors. Belongs to the plant acyltransferase family.