How to post to custom systems

i'm pretty sure you can upload more than 4, i heard the devs implemented that feature into this game and site too (it originated from SP) but it didn't work due to some reason so they disabled it, though that was a fairly long time ago so maybe they have since fixed and re-enabled it?
@SamTheFox

first, you need to upload all the planets/moons/asteroids/stars in the system
second, you need to upload the system itself

you can upload any craft (or planet/system in this case) by loading the body in PlanetStudio, then tap the upload button in the PlanetStudio menu on the left. if you can't find the menu, tap the icon with 3 horizontal lines on the top left

remember that you can only upload 4 things (whether it be a planet, craft, system, etc) in 1 day, so make sure you upload it unlisted

@CORC and how u do that?