A "3D" error is a rejection/failure by the reader because the mirror test failed.Either the mirror or optical path has issues, someone tried the wrong flat hand, someone was lifting their hand and failing the test.If there are many of these errors on more than a couple of people, than they should run some diagnostics on the unit to check if there is an issue with the camera.If it's just one person who is consistently generating that error, then we need more information and an image of his/her placement.You can try telling them to keep their hands flat.
Can also try to clean the reader where they place hand and the mirror above if the above fails. Then try again.
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