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Turning on the Custom transaction numbers feature helps to change the number of previous invoices. Once done, we'll see an Invoice no. field where you can enter your own numbering preferences. We can also open the past invoices and modify the number.
The sequence you set here applies to all sales forms. If you'll want QuickBooks automatically assign numbers to your sales forms, just turn off this feature. On the other hand, the option to set a unique numbering of credit notes is unavailable. What we can do is to manually change the number sequence on the transactions. For additional reference, you can go through these articles:
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