Client Invoice Definitions
Void = Creates a negative invoice transaction to reverse the original transaction. You cannot Void an Advance Bill.
Write Off = Typically used if the client is not going to pay for the invoice. This will create a credit memo and apply the "Open Amount" on the invoice and post to your Bad Debt account.
Close = Used to recognize the unused portion of an Advance Bill and creates a new regular invoice to post the Unapplied Amount to your sales.
Create Credit = Converts the "Unapplied Amount" of the advance bill to be a credit memo, so it can be printed and sent to the client to use against future client invoices.
Post = This affects the General Ledger based on the Posting Date of the transaction.
Approve = Helps to separate workflow from accounting procedures.
#1, if they collect sales tax on the adv bill, then it can only be applied against the future sales tax. So, their regular invoice must have a sales tax amount matching the tax code as the adv bill in order to fully apply the tax amount collected on the AB to the regular client invoice.
If they simply included all as part of sales on the AB, then that amount can be applied against sales or tax on the regular invoice.
#2, Close will create a regular client invoice and apply the AB against it. Create Credit will create a regular client invoice to apply against it and create a credit memo based on the unapplied amount of the AB. The credit memo can then be applied against future invoices.