Hi Trevor2,
Thanks for posting. You can use the Banking reconciliation report to work out how much you need to top up your petty cash to get it back to its required balance (Reporting menu > Reports > Banking reconciliation). For full details and instructions on how to deal with this, you may check out this helpful article about dealing with petty cash.
Feel free to start a new post again if you require any assistance.
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Kind regards,
Shella