What does E3 mean on the control panel display?
E3 indicates that the carriage inside the printer has stalled. To resolve, open the front door, then the printhead access door, ensure the printhead latch is closed properly and remove any jammed paper or objects blocking the carriage before closing both doors again and pressing the Resume button to continue printing (Page 10).
From the official HP Smart Tank 750 manual, page 10
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