Make shure that you have completed preparation steps (easiest way, still easy way or advanced way):
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3473996451

1. Replace numbers with your mod name
   
   id = "3473996451,"
   
   Done. You can upload now. Other edits are optional, but highly recommended. Go to the "Final steps" if you are not interested
   
   
2. Replace with the same mod name as you used above
   
   name = "Your mod name",
3. Replace with the same mod name as you used above
   
   title = "Your mod title",
4. Replace with short description text
   
   description = "Your mod description",
5. Replace to 1.1 or 1.0.1 in the future, if you decide to update
   
   version = "1.0",

1. Make shure that there is only one "packList.lua"
   "packList_hard.lua" should be deleted
   
2. Make shure that there is only 1 folder with races inside data/textures/realCaptains2
   "hardFolder" and "packName" folders should be deleted

1. I recommend 960x540 thumb.png
   
2. If you get an error while uploading, probably thumbnail has too high resolution or weight. It got me several times

1. Make shure that you are still here C:/Steam/steamapps/workshop/content/445220
   
2. Replace mod folder name "3473996451" with your mod name
   
3. Copy your mod
   
4. Go to C:/Users/YOUR_USERNAME/AppData/Roaming/Avorion/mods
   
5. Paste your mod here, in "mods/" folder
   
6. Launch Avorion
   
7. Settings --> Mods --> "Upload To Workshop"
   
8. Choose your mod, hit "Upload"

Note: if you will be developing more mods, do not keep them in the steam workshop folder, as your changes will be deleted when mod author makes an update. Move them to "AppData/Roaming/Avorion/mods" for safety