Once you connect erplain with QuickBooks, all invoices created from erplain will be created in QuickBooks just like if you had created them directly in QuickBooks.
You can choose to send these invoices automatically by checking the following option in the integration settings (menu Apps > Configure QuickBooks > Documents).
If this option is not enabled, you will see a "Send to QuickBooks" button in the invoice to send the invoice to QuickBooks:
If you have enabled the option to send automatically and still see the "Send to QuickBooks" button, this means that QuickBooks rejected the invoice. You can click on the "Send to QuickBooks" button, you will see the related error message. You can find the list and solutions of QuickBooks error messages on this page.
Once the invoice is sent to QuickBooks, you will see the QuickBooks logo in the invoice and the QuickBooks status. You can click on the logo to open the invoice in QuickBooks.
If you create an Invoice in QuickBooks, this invoice will not be created in erplain but QuickBooks will send an Inventory adjustment to erplain to keep your Inventory in sync between the 2 systems (unless the option 'block inventory updates from QuickBooks to Erplain' is active)
You can add payments directly in erplain or in QuickBooks if you prefer. Payments added in erplain will be synced to QuickBooks and attached to the invoice. If you add the payment in QuickBooks, it will update the QuickBooks status of the invoice, but the payment will not be synced to erplain.
Cancelling the invoice
Cancelling the invoice in erplain will void the invoice on QuickBooks. Once an invoice is cancelled, you can't re-activate it.
Updating the invoice
Note that invoices are synchronized only from erplain to QuickBooks. If you update an Invoice erplain it will update the invoice in QuickBooks, but if you update the invoice in QuickBooks it will not be updated in erplain.
You can find more details on the integration settings in the QuickBooks settings page.