Well mystery solved i guess, cargo says 4/4 and its full with other things. Fell silly now. So i guess cant run cargo mission with the sidewainder, correct?
You can do
everything with a Sidewinder - it's the smallest multi purpose ship in the game!
Ok, in your case, you have 4 tons of cargo capacity, which are already taken up with other things. So you need to get rid of these other things (sell or dump them - just don't dump them inside a station
), then load up with 4 tons of your mission cargo, deliver, return, rinse, repeat.
Or go to outfitting and refit your sidewinder for cargo hauling - set up for cargo only,
you can fit 16 tons in there. You just have to be a bit careful, as this means you'll need to leave your shields behind.
Or earn a few thousand credits, then switch over to the aptly named Hauler. That can fit 16 tons of cargo, a shield and 3 smaller items, like scanner or auto pilots.