When an order or invoice cannot be created due to existing consecutive number, you should check the next number to take and change it.
On the device, you may go to Main Menu > Database > Sales/Invoices > press the gear icon > Sales > Next Order Number > Change on the suffix box > Done or Invoice > Next Invoice Number > change on the suffix box > Done
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On the web version, Database > Sales/Invoices > gear icon > Next Order Number or Next Invoice Number > Save
Click on Settings
Change the Next Order or Invoice numbers
On the device you should go to Database > Sales/Invoices > Settings > Sales orders > Nerxt order number
Database
Sales/Invoices
Settings > Sales orders
Next order number
Change the suffix then Done
Settings > Invoices
Next Invoice Number
Change the suffix then done
Now if you need to change the label on the PDF Invoice, tap on the invoice box and then done