If you are applying payment to an Order through the portal or through the Process Payment Wizard, then an Invoice will automatically generate. You can also adjust your settings to automatically generate Invoices for certain Order type. However, if an Invoice is not created, you can manually create one via an easy button press.
1. Open the Order record that needs an Invoice generated.
3. The Invoice will be created automatically. All of the fields filled out in the Order will auto-populate in the Invoice as well.
Note that the system must create the Invoice through the button. Attempting to create the record manually will not also create the connection between the Order and the Invoice. This can cause problems when applying payment or if one of the records gets updated.