I got via version 3.0 and via backwords 3.0 and it says that it can't load viarewind

You are using the DEV branch right? 'Cause that's the one you should use along the Abstraction branch of ViaVersion (ViaBackwards as well).

You are using the DEV branch right? 'Cause that's the one you should use along the Abstraction branch of ViaVersion (ViaBackwards as well).

Already changed and now it load and i try to join a spigot 1.13 in 1.8 but it won't work

Please run /viaversion dump in-game or in your console and provide us with the link, it gives us useful information about your server.

You are using the DEV branch right? 'Cause that's the one you should use along the Abstraction branch of ViaVersion (ViaBackwards as well).

Already changed and now it load and i try to join a spigot 1.13 in 1.8 but it won't work

Hmmm, wierd. Just tested it with Paper 1.15.2 (build #350) and it worked. Also tested with the latest build of Spigot 1.13.2, and worked as well. Here is a screenshot.

@notImAle So were you able to solve it? If not, you should post the dump.