When creating an invoice QuickBooks normally takes the last number recorded and increments it by one but now it's giving me an already existing number how to correct?

Hi slabreche@turner,

It's a pleasure to see you in Community.  Welcome!  Having previously used reference numbers on your invoices is concerning.  QuickBooks Online enables you to reset the sequence, to ensure your forms remain accurate and organized.  I'd be happy to help!

When you create a new invoice, simply enter the next number in the Invoice no. field.  Once you save the invoice it should retrigger the sequence and prevent manual entry on the next invoice you create.  

Give that a try and let us know!  We'll be a message away, if you have other questions or concerns!