Thanks for posting here in the Community. I'm here to help share information about how invoice/sales forms numbering works in QuickBooks Online (QBO).
When creating an invoice/sales forms, QB assigns the transaction numbers automatically to help you identify transactions easily. Since you have amended a sales invoice, the next entry will automatically follow the number in sequence with the last invoice. You can also reset your transaction numbers to suppress this activity. Here's how:
Click the Custom transaction numbers checkbox, then Save.
Create a transaction with a new starting number.
Clear the Custom transaction numbers checkbox, then click Save.