How do I modify the auto-generated invoice number for the new financial year? 

You can modify the auto-generated invoice number easily. 

• Go to the Invoices module in the left sidebar. 
• Click the + New button in the top right corner. 
• Click the  next to the Invoice# field. 
• Edit the prefix of the invoice number based on the new financial year’s sequence. For example, if you’ve been using INV17-xxxx, you can change it to INV18-xxxx. 
• Click Save. 

Now, the invoice number will auto-generated with the new prefix for every new invoice.