Postgres - trigger logging, but also record single value of row

I am very new to PostgreSQL.

I currently using the following code (from Use a Postgres trigger to record the JSON of only the modified fields) to log changes to tables

declare
    json_new jsonb;
    json_old jsonb;
begin
    if tg_op = 'INSERT' then
        json_new:= to_jsonb(new);
    elsif tg_op = 'DELETE' then
        json_old:= to_jsonb(old);
    else
        select jsonb_object_agg(new_key, new_value), jsonb_object_agg(old_key, old_value)
        into json_new, json_old
        from jsonb_each(to_jsonb(new)) as n(new_key, new_value)
        join jsonb_each(to_jsonb(old)) as o(old_key, old_value) 
        on new_key = old_key and new_value <> old_value;
    end if;
    insert into logging.t_history(tabname, schemaname, operation, old_val, new_val)
    values (tg_relname, tg_table_schema, tg_op, json_old, json_new);
    return null;
end;

I'd like to be able to also record the unique 'refno' of the row that's been changed.

I have tried declaring the value, probably incorrect....

declare
    json_new jsonb;
    json_old jsonb;
    refno varchar;
begin
    if tg_op = 'INSERT' then
        json_new:= to_jsonb(new);
    elsif tg_op = 'DELETE' then
        json_old:= to_jsonb(old);
    else
        select jsonb_object_agg(new_key, new_value), jsonb_object_agg(old_key, old_value)
        into json_new, json_old
        from jsonb_each(to_jsonb(new)) as n(new_key, new_value)
        join jsonb_each(to_jsonb(old)) as o(old_key, old_value) 
        on new_key = old_key and new_value <> old_value;
    end if;
    insert into logging.t_history(tabname, schemaname, operation, old_val, new_val, refno)
    values (tg_relname, tg_table_schema, tg_op, json_old, json_new, refno);
    return null;
end;

However I get the following error:-

Could not commit changes to layer

Errors: ERROR: 1 attribute value change(s) not applied.

Provider errors: PostGIS error while changing attributes: ERROR: column "refno" of relation "t_history" does not exist LINE 1: ...ory(tabname, schemaname, operation, old_val, new_val, refno) ^ QUERY: insert into logging.t_history(tabname, schemaname, operation, old_val, new_val, refno) values (tg_relname, tg_table_schema, tg_op, json_old, json_new, refno) CONTEXT: PL/pgSQL function change_trigger2() line 17 at SQL statement

The changes are being made through PostGIS - first trigger works fine but second fails.

Any assistance would be really appreciated! Thank you in advance.

EDIT:-

I managed to declare the value of refno by using the old and new values and adding old_refno and new_refno columns to the logging table. However my preferred option would be a single refno column that held old and new depending on which one was present

declare
    json_new jsonb;
    json_old jsonb;
    old_refno varchar := old.refno;
    new_refno varchar := new.refno;
begin
    if tg_op = 'INSERT' then
        json_new:= to_jsonb(new);
    elsif tg_op = 'DELETE' then
        json_old:= to_jsonb(old);
    else
        select jsonb_object_agg(new_key, new_value), jsonb_object_agg(old_key, old_value)
        into json_new, json_old
        from jsonb_each(to_jsonb(new)) as n(new_key, new_value)
        join jsonb_each(to_jsonb(old)) as o(old_key, old_value) 
        on new_key = old_key and new_value <> old_value;
    end if;
    insert into logging.t_history(tabname, schemaname, operation, old_val, new_val, old_refno, new_refno)
    values (tg_relname, tg_table_schema, tg_op, json_old, json_new, old_refno, new_refno);
    return null;
end;