Starting July 14th, Roblox will be reducing what creators earn from 2D items, from 70% to 30%. If sold in-game, the game developer will earn 40% and the creator will still earn 30%.
In addition, to upload either 2D or 3D items, you need to pay 200 Robux and be ID verified (or have a linked parent account). To upload, you will need an active Plus/Premium membership and pay a publishing advance, starting at 600 Robux. Totaling to 800 Robux, minimum, per item.