My ISP says 4d2.sh is a malware site / my work firewall blocks 4d2.sh.
This is an unfortunate consequence of running a service that allows unrestricted uploads. Apps like 4d2.sh are commonly marked as malware sites in corporate filter lists, which are commonly used by corporate networks and in some cases by especially heavy-handed residential ISPs. This is their decision and not something we're able to change.