!!
critical HP
Error Code Attention light on with E7 and Ink icons blinking
One or more ink tanks are out of ink. Ink tank(s) are completely empty and printing cannot continue.
? What Causes This
Ink tank(s) completely depleted.
✓ How to Fix It
Refill the indicated ink tank that is out of ink.
Source: page 18 of the official manual
From the manual
This error code appears in:
HP Smart Tank 6000 Printer