No worries, this can happen sometimes. Here are some tips how to get the picture to work.
Step by Step:
1) Make sure that you have selected the correct issuing country in the grey area above before starting the scan.
2) Make sure that you have selected the correct document type.
3) Put your ID card/passport on a flat surface and started the scan from further away, slowly getting closer to the document.
4) Align the document with the lines in the scanning screen. They should match the edges of your document.
Should this not be possible, please keep an eye out for an error message and contact our support via firstname.lastname@example.org to get a hand.