Hello, holly53. Thank you for bringing up your concern about the invoice number repeating. I recognize the importance of having accurate invoice numbers.
Before we move forward, I need to gather a bit more information about the issue. Do you have another user who is responsible for managing your invoices? Is there a chance that some invoices were deleted accidentally?
If the no. of invoices accidentally changes with the same number and Yes is selected at the prompt, it could lead to the duplication of invoices.

To correct or adjust the sequence of invoice numbers, it is advisable to manually update any incorrect numbers to maintain the correct order. Additionally, consider disabling the custom transaction numbers feature to prevent similar issues in the future.
Once everything is in order, you can begin to review the receive payment function in QuickBooks Online. For guidance, please refer to the article: Receive and process payments in QuickBooks Online with QuickBooks Payments.
If you have any additional questions regarding invoices in QBO, feel free to leave a comment below. I'm here to assist you.