Hello DC,
By "not showing up", do you mean it's not visible on the account? (Is it in history?) or do you mean that the AR balance outstanding hasn't changed? (Was the batch posted? Is the transaction visible in the general ledger?)
Print preview a customer transaction report for all customers, all transactions and search the report (use the field next to the binoculars at the top of the print preview screen) for something that would identify the transaction. Perhaps it was posted to the wrong customer.
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Andrew Bates