There are two ways to set up Unapplied Cash to Auto Apply for specific Invoice Types.
Payment Processing
When entering a Payment in Payment Processing as Unapplied Cash you have the option to enter a portion or the full amount of the payment and select which Invoice Type(s) the Unapplied Cash will automatically be applied to when that invoice is created and saved.
Customer Account
If a Customer Account has Unapplied Cash on their Account, you can right click on that Item and select Auto-Apply.
Select the Other Tab and Unapplied Cash.
The Setup Auto Credit will open and if the Unapplied Cash was previously set up to be automatically applied to a specific Invoice Type, that box will be selected.
If none of the boxes are selected, then you can mark which Invoice Type(s) you want the Unapplied Cash to be automatically applied to when that invoice is created and saved.