3GPP 24.501 v20.0.0 — the document's own text
8.2.10.8 MA PDU session information
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
The UE may include this IE if the Request type IE is included and is not set to "initial emergency request " or "existing emergency PDU session" in the UL NAS TRANSPORT message.