"Works that cannot be recovered by readers . . . are cited in the text as personal communications."
"Because readers cannot retrieve the information in personal communications, personal communications are not included in the reference list; they are cited in the text only."
"Give the initial(s) and surname of the communicator, and provide as exact a date as possible."
Examples:
E.-M. Paradis (personal communication, August 8, 2019)
(T. Nguyen, personal communication, February 24, 2020)
(Publication Manual of the American Psychological Association, 2020, p. 260)