Hi Rob,

To start with, if you haven't seen it, here's a guide & video from our Help Centre: Updating your conversion balance.

The conversion/opening balances should be entered as at what sounds like 31 July (if client has been using Xero since August) - including all bank and other balances from a trial balance or previous system.

If there were outstanding payable and receivable invoices at that date, enter each outstanding balance on the Conversion Balance screen then you'll be prompted to enter the outstanding invoices that make up each balance.

If it happens that your client already entered those invoices into Xero and used the actual invoice date (i.e. a date prior to the conversion date), they'll be counted towards the AR/AP conversion balance when you enter it, and any imbalance means you'll have missing transactions to enter. If the invoices from before the conversion date are entered with a date after the conversion date there'll be some unwinding to do to get them dated prior to the conversion date so that they can be included in the relevant AR/AP conversion balance.

This is a really quick and basic take on the situation without seeing what's going on. We have some really helpful and knowledgeable Xero accounting partners on our Business Community so you'd benefit a lot from asking your question on that forum as well if you're not getting the help you need from my response. For example, here's a discussion on changing the conversion date after a client has already started using Xero themselves - a slightly different situation to what you're talking about but some great information about how the conversion date works as explained by accountants using Xero: Changing the Conversion Date & the impact on transactions already entered

Of course you're also welcome to email our Customer Care team on support@xero.com