3GPP 24.501 v20.0.0 — the document's own text
8.2.19.15 Configured NSSAI
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
The AMF shall include this IE when the AMF needs to provide the UE with a new configured NSSAI for the current PLMN or SNPN and the UE is neither registering nor registered for onboarding services in SNPN.