Oracle Database Discussions

I'm trying to create an SDO_GEOMETRY spatial index in Oracle Live SQL (https://livesql.oracle.com/):

CREATE TABLE ply (objectid     NUMBER(*,0), 
                  query_source NVARCHAR2(255),
                  shape        SDO_GEOMETRY);
INSERT INTO user_sdo_geom_metadata (table_name,column_name,diminfo,srid) 
VALUES (
   'ply',
   'SHAPE',
   sdo_dim_array(
       sdo_dim_element(NULL, 1, 100, 0.001), 
       sdo_dim_element(NULL, 1, 100, 0.001)
   ),
   26917
   );
CREATE INDEX ply_shape ON ply (shape) INDEXTYPE IS mdsys.spatial_index;

But I'm getting an error:

ORA-29855: error occurred in the execution of ODCIINDEXCREATE routine ORA-06512: at "MDSYS.SDO_INDEX_METHOD_10I", line 10

Why am I getting that error?

Unfortunately, I can't seem to save/share my Live SQL session due to an error:

But the SQL does work in db<>fiddle: https://dbfiddle.uk/KqGs8_uZ. And it works in my on-prem Oracle 18c database too.

Any ideas? Thanks.

Edit:

I was able to eventually save the Live SQL script:
https://livesql.oracle.com/apex/livesql/s/oyvnm2jx4akuczwt1durh8124