I tried running this script, but i kept getting not a group by error

select
  a.*,
  b.Start_Date,
  b.End_date,
  sum(b.cost) as total_Cost
from Ess.TZeewrld a
left join Ess.Wrldest b
  on a.account_number, = b.account_number,
group by
  b.Start_Date,
  b.End_date;