How to set your own jar on a Minecraft server
Before loading your server you need to make sure you have a jar or the correct jar set on the overview page. If you’re using the version or modpack installer, the correct jar should be set for you. However, if this is not the case, or you have uploaded your own jar to the server, please follow these steps.
Setting The Jar
Setting the jar is simple. Head to the overview page and type the name of the jar you want to load into the Server Jar File box.
Knowing What To Set
If you’re not sure what this should be set to, head to your file manager. Here you’ll be able to see any jars installed on your server. Look for the one you would like to load, copy its name, and past it into the Server Jar File box.
Forge & Fabric
In the case of Forge and Fabric, you will have more than one jar in your file manager. A common mistake, in this case, is to choose the minecraft jar.
When using forge and fabric make sure you’re loading the forge/fabric jars, otherwise, your mods will not load.