help needed Servers using previous versions?

[KrunkhyToast]

I'm trying to import a 1.12.2 world into the dashboard and it doesn't seem to be working. The world file (ZIP) is pretty large and takes a while to gain % on the uploading, so i just leave for a while and come back to it showing: Upload World (next line) Upload a world to your server. (three lines down) No file selected. [Choose File]

I joined the server in 1.14.3 but nothing is there from the world i'm importing.

How can i convert my server to 1.12.2?

[KrunkhyToast]

To keep it from corrupting*

[Minipixel]

When you upload a world you can restart, and do /worlds the name will show up. If it's crashing when you click on the world saying Illegal Characters try deleting the world and rename the folder from your end of the computer and the folder inside of the .ZIP 

[Minipixel]

If that doesn't work Contact Support