Invoicing is handled by your favorite solution and generated invoices are recorded as receivables on Bkper through automations. This way balance values of your receivables always show the actual value to receive.  

There are great online invoicing solutions available such as ZipBooks, Invoice Ninja, Zoho, Yamm and many others that easily connect (without programming) through automations such as the Google Sheets Add-on for Bkper.

The Bkper API helps you customize and extend Bkper into G Suite so you can quickly build your own solutions and automate workflows such as invoicing with very simple Google Apps Scripts that fully integrate with G suite.