noun which may take the genitive case particle 'no'
interpersonal; between individuals
Used as a no-adjective to describe something happening or existing between private individuals, as opposed to between organizations or in public contexts.
Lending and borrowing between individuals can easily lead to trouble.
I use a site for person-to-person buying and selling.
対人 is also 'interpersonal' but often used in contexts like 対人関係 (interpersonal relationships) or 対人恐怖症 (social anxiety). 個人間 emphasizes the private, non-institutional nature of the interaction.
interpersonal communication
interpersonal messaging service
Compound of 個人 (individual) and 間 (between, among).