QuickBooks Online is designed with awesome features to make it easy for you to handle your business. Having the flexibility to edit your numbering system for your invoices is essential. I'll be happy to assist you with this.
QuickBooks automatically assigns numbers to your sales forms starting with 1001. If you'd rather use your numbering format, here's how to proceed.
Go to the Gear icon then Account and Settings (or Company Settings).
Select the Sales tab, then click anywhere within the Sales form content section.
Check the box next to Custom transaction numbers.
Select Save and then Done.
Open an invoice or any sales form, and in the Invoice no. field, enter the custom number or letter sequence you want to use for your forms.