When creating or editing an invoice, if there are other invoices available for merging, a message will be displayed at the top of the screen.
You can merge multiple invoices by selecting the checkbox next to each invoice number. Once selected, the invoice items from those invoices will be automatically included in the invoice you are currently working on.
Additionally, instead of deleting the merged invoices, you have the option to mark them as Cancelled. This is recommended to avoid gaps in your invoice number sequence. If keeping a continuous invoice number history is important to you, it's best to avoid merging. Alternatively, you can manually adjust the invoice numbers to maintain sequence consistency.