First you must install/downgrade the corresponding Minecraft version for your modpack.
This step is very important
To do this:
Start by deleting all the files in your Files tab so you have a clean slate.
Then in your Startup tab, set the Minecraft version to the one from your modpack in the Server Version box in the Startup tab (eg a 1.18.2 based modpack, change from latest to 1.18.2)
Then run a Reinstall from the settings tab.
After that, follow the relevant modpack type below.
Ensure you complete the “Installing the corresponding Minecraft version” step
Download the relevant server pack
Upload the server pack to the server, ensuring mods go into the mods folder
Select Forge Java 17 (1.18.x+ Forge only) in the Docker Image section on the Startup tab
Unfortunately there's no consistency with Forge packs, so if any installation or files are missing, then reach out to our support team for assistance as the reliability of each pack varies greatly
Ensure you complete the “Installing the corresponding Minecraft version” step
Download the relevant server pack
Upload the server pack to the server, ensuring mods go into the mods folder
Ensure SERVER JAR FILE references the correct forge.jar
Unfortunately there's no consistency with Forge packs, so if any installation or files are missing, then reach out to our support team for assistance as the reliability of each pack varies greatly