3GPP 24.501 v20.0.0 — the document's own text
8.3.3.8 ATSSS container
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
The network may include this IE to indicate the reason for the failure of the MA PDU session establishment procedure as specified in 3GPP TS 24.193 [13B].