select
  iif(s.bundle_id is not null, 10, coalesce((select 3 from ta_bundle b where b.submit_slot_id = s.id and b.status_id = 3 rows 1), 1)) as status_id
from ta_submit_slot s
where s.submit_id = :submit_id
group by 1

Invalid token.
Dynamic SQL Error.
SQL error code = -104.
Invalid expression in the select list (not contained in either an aggregate function or the GROUP BY clause).

select
  iif(null is not null, 10, coalesce((select 1 from rdb$database rows 1), 1)) as status_id
from rdb$database s
group by 1

select
  iif(s.rdb$relation_id is not null, 10, coalesce((select 3 from rdb$database b), 1)) as status_id
from rdb$database s
group by 1

select
  iif(s.bundle_id is not null, 10, coalesce((select 3 from ta_bundle b where b.submit_slot_id = s.id and b.status_id = 3 rows 1), 1)) as status_id,
  count(*)
from ta_submit_slot s
where s.submit_id = :submit_id
group by 1

select
  iif(s.bundle_id is not null, 10, coalesce(5, 1)) as status_id,
  count(*)
from ta_submit_slot s
where s.submit_id = :submit_id
group by 1

select
  iif(true, 10, coalesce((select 1 from rdb$database rows 1), 1)) as status_id,
  count(*)
from ta_submit_slot s
where s.submit_id = :submit_id
group by 1

select
  case
    when (s.bundle_id is not null) then 10
    else coalesce((select 3 from ta_bundle b where b.submit_slot_id = s.id and b.status_id = 3 rows 1), 1)
  end as status_id
--  , count(*)
from ta_submit_slot s
where s.submit_id = :submit_id
-- group by 1

  case s.bundle_id
    when (not null) then 10

with tmp as (
  select iif(s.bundle_id is not null, 10, coalesce((select 3 from ta_bundle b where b.submit_slot_id = s.id and b.status_id = 3 rows 1), 1)) as status_id
  from ta_submit_slot s
  where s.submit_id = :submit_id)
select t.status_id, count(*)
from tmp t
group by 1