media url for doi entries are limited to 255 characters (see https://github.com/datacite/mds/issues/297). If URL is longer we get an Internal Server error. At datacite the DOI entry exists, but mycore has no entry in database. We should leave the media entry empty and add DOI information nevertheless into our database. User should get an information about this problem, so that he can rename the file.
Alternatively we could check the URL and if it is to long user get this information and can not register DOI until he renamed the file ...