This could happen for one of several reasons.
Please check to make sure that your ID is legible and is one of the acceptable forms listed.
Other factors, such as lighting and camera resolution can sometimes make scanning the ID difficult; the ID should scan without issue and the information should be legible on your computer screen.
If declined, try to scan the ID again, or upload it manually.
If the issue still persists, please reach out to us by raising a support ticket and we'll get back to you as soon as we can.