Yes, your father needs to pay you--at least minimum wage--unless you are an owner of the business. All non-owner workers, including adult family members, must be paid for working; there is no legal "volunteer" or unpaid work. Since being paid will result in social security contributions for you and potentially make you eligible for unemployment in the future should you stop working for him, this is not a bad thing; and you can turn around and pay "rent" to your father or gift him the money if you don't want to keep it.