Hi there, love the game. I made many shipping contracts already. Works really nice, especially now with auto-provisioning.
What I managed to do recently was, I made shipping contract to nowhere. Meaning - I screwed up target planet location (a instead of b) and that turned into messy situation. I then tried to somewhat fix the problem - turns out - you can’t deliver from ship to ship.
Maybe since you need some storage (base or WAR) at source and destination, seem that there could be a warning if you are about to make such mistake (making shipment contract while lacking storage at destination).