To be able to generate an Invoice Number the bill split must be finalised.
When the bill split has a Zero value, the Finalise button will appear.
When clicking on Finalise, no further changes can be made and an invoice number is generated.
If there are any bill splits that are NOT finalised, the Check Out button at the bottom right will Finalise them automatically, providing each split has a zero value.
Clicking on 'View' will allow you to print or send a copy of the bill with the invoice number now generated to the guest.