Can't grant execute grant with rdsadmin.rdsadmin_util.grant_sys_object over SYS.VALIDATE_APEX

I need to execute sys.validate_apex in order to make SPATIAL works on Oracle APEX. I tried the following code:

begin
    rdsadmin.rdsadmin_util.grant_sys_object(
        p_obj_name  => 'VALIDATE_APEX',
        p_grantee   => 'SNW_SYSTEM',
        p_privilege => 'EXECUTE');
end;
/

With the consequent error:

Error report -
ORA-20199: Error in rdsadmin_util.grant_sys_object. ORA-20900: You do not have permission to grant: EXECUTE to SYS object: VALIDATE_APEX
ORA-06512: at "RDSADMIN.RDSADMIN_UTIL", line 255
ORA-20900: You do not have permission to grant: EXECUTE to SYS object: VALIDATE_APEX
ORA-06512: at "SYS.RDS_SYS_UTIL", line 513
ORA-06512: at "RDSADMIN.RDSADMIN_UTIL", line 252

The root problem is caused by adding SPATIAL option after APEX-DEV option.

Any page in my apex applictaion related to SPATIAL datatypes returns error:

ORA-06592: No se ha encontrado la opción CASE al ejecutar la sentencia CASE

I tried editing the Option parameter group so it could trigger the procedure without success.

Any help is welcome. Thanks!