SQL> create table IOT_MAPPING_TEST (name varchar2(32),
  2                                 no number,
  3                                 constraint PK_IOT_MAPPING_TEST primary key(no)
  4                                 )
  5  organization index
  6  mapping table;

Table created

SQL> 
SQL> select table_name,iot_name,iot_type from user_tables where table_name='IOT_MAPPING_TEST';

TABLE_NAME                     IOT_NAME                       IOT_TYPE
------------------------------ ------------------------------ ------------
IOT_MAPPING_TEST                                              IOT

SQL> select table_name,iot_name,iot_type from user_tables where iot_type='IOT_MAPPING';

TABLE_NAME                     IOT_NAME                       IOT_TYPE
------------------------------ ------------------------------ ------------
SYS_IOT_MAP_56839              IOT_MAPPING_TEST               IOT_MAPPING

SQL> 
SQL> alter table iot_mapping_test shrink space;

Table altered

SQL> alter table SYS_IOT_MAP_56839 shrink space;

alter table SYS_IOT_MAP_56839 shrink space

ORA-28668: cannot reference mapping table of an index-organized table

SQL>