3GPP 24.501 v20.0.0 — the document's own text
8.2.30.2 CIoT small data container
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
This IE shall be included if the UE needs to send uplink small user data, SMS or location services message that is not more than 254 bytes, and there is no other optional IE to be sent.
NOTE: When the UE determines to use the CIoT small data container IE to send uplink data in this message, there is no other optional IEs in this message.