Please read the email we have sent you. It explains the reason for the rejection. In fact, there can be even several reasons.
The most frequent reasons are uncovered sensitive data; no signature on the back of the card; a cropped photo where some of the corners and edges are not seen.
For the sake of your security, we ask you to hide a part of the card number on the front and back of the card, leaving only the first 6 and the last 4 digits. Also, you need to hide the CVC2 / CVV2 code on the backside.