3GPP 24.501 v20.0.0 — the document's own text
8.2.9.15 Extended 5GMM cause
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
This IE may be included by the network to indicate additional information associated with the 5GMM cause value #15 "no suitable cells in tracking area".