Problem structured type in a procedure

I've created a table using CDS that uses a structured type.  This is a simplified example I've created to experiment:

namespace f14e.S001.GBI.data;
@Schema: 'MYSCHEMA'
context new  {     type TestType2        {            A : String(1);            B : String(1);        };    @Catalog.tableType: #COLUMN    entity TEST {    key ID  : Integer;    TEST : TestType2;     };       context procedures{                type testStructure {            ID : Integer;            TEST : TestType2;        };                type errorsStructure {            HTTP_STATUS_CODE : Integer;            ERROR_MESSAGE : String(100);            DETAIL : String(100);        };    };
};

Now I want to use a procedure to handle the create operation with an oData service.  This is the procedure:

PROCEDURE    "MYSCHEMA"."f14e.S001.GBI.data::createTest" (        IN intab "f14e.S001.GBI.data::new.procedures.testStructure",        OUT outtab "f14e.S001.GBI.data::new.procedures.errorsStructure"    )  LANGUAGE SQLSCRIPT  SQL SECURITY INVOKER AS   --DEFAULT SCHEMA <schema>  --READS SQL DATA AS
begin
declare lv_id string;
declare lv_a string;
declare lv_b string;
select ID, "test.a", "test.b"
into lv_id, lv_a, lv_b from :intab;
if :lv_id = '' then  outtab = select 500 as http_status_code,               'Invalid ID '  as error_message,
'No Way! ID field must not be empty' as detail from dummy;
else   insert into "f14e.S001.GBI.data::new.TEST"         values (lv_id, lv_a, lv_b);
end if;
end;

The error I get when activating this is:

[07:02:40] Error while activating /f14e/S001/GBI/data/createTest.hdbprocedure:

Could not create catalog object: invalid column name; test.a: line 15 col 12 (at pos 402)

I've a variety of variations to get this work and I'm beginning to wonder if it's possible.  Should I move on and drop the structured type?

Thanks,

Ross