Hi bbscleantidy,
Totally get how that’d be a bit confusing, especially when you’re still getting set up as a new business.
In AccountRight desktop, whether the order number is kept or changed when you convert a sales order to an invoice is controlled by a Sales preference.
It sounds like you currently have the option turned on to keep the original number. To have the invoice use the next invoice number instead of the SO number, do this:
Go to Setup > Preferences.
Click the Sales tab.
Untick: Retain Original Invoice Number when Quotes Change to Orders or Invoices
Click OK to save.
For more detail on changing sales types and numbering, see: Changing a sale’s type (AccountRight)
I hope this helps!
Regards,
Earl