* To enable the invoices automatic generation, enable the developer mode,
  go to Settings > Automation > Scheduled Actions
* Filter the archived actions and activate 'Generate Standard Invoices'.
* Adapt the frequency you want to automatically generate invoices to your needs.
* The field 'Next Invoice Date' on partner form indicates when the next invoice
  generation will take place.
* To manually change the invoicing group (one invoice per order), go to the
  Sale Order > Other Information > Invoicing and Payments and check
  the 'One Invoice Per Order' box.