Minecraft Fabric Server Crash?

Does anyone know why my Minecraft 1.16.5 Fabric Server won't start without mods? I'm sorry that I can't copy or paste a log because no log or crash report was created. Copying is also not possible on a cell phone. That's why I'm adding a screenshot. That's the whole log too.

Did you install fabric per function from your server provider? Which is that? Ask their support.

All good, I already fixed it. I'm sorry I couldn't answer until 3 days later. I had to rename the normal vanilla jar to "vanilla.jar" and the fabric jar to "custom.jar", although Server.jar is specified in the "Startup" tab. I use gameserver.gratis.