Focus on the pronunciation of sub
English definition of “sub”
/sʌb/ noun [C] informal
› subscription: You can save up to £20 if you pay your subs by direct debit.
› substitute noun: There is a great need both for permanent teachers and subs.
› payment that your employer gives you earlier than usual because you need money: I ran out of money on Thursday and had to ask my boss for a sub.