To use the forge version of Sponge plugin manager ("SpongeForge") alongside a forge modded minecraft server requires one extra step, after the One Click installer has finished installing the selected Modpack and correct version of Forge.
It will be necessary to manually download the version of SpongeForge needed, and then upload it to your server. This guide will help you with that process.
Navigate to https://www.spongepowered.org/downloads/spongeforge/stable/1.12.2,
This will bring you automatically to the 1.12.2 version of SpongeForge, but you can select older versions in the "minecraft version" dropdown menu in the upper right corner of the page. The oldest version of minecraft that SpongeForge is compatible with is 1.10.2. Versions of minecraft older then this will require different plugin managers.
Select the recommend version of SpongeForge that matches the version of the Forge jar installed with the modpack.
Download the file.
Open the file manager on your server control panel, and then navigate to the
/modsfolder. Upload the SpongeForge file to the
/modsby dragging and dropping into the file manager window.
We also offer a SpongeForge plugin manager in NodePanel! Use the "plugins manager" tab on the left side of your server control panel to download and install plugins. You can also find plugins via the Sponge Ore platform at https://ore.spongepowered.org/.
There are different plugins for Sponge, and plugins for other managers such as Bukkit will not be compatible with Sponge.
Troubleshooting: if the wrong version of SpongeForge was downloaded, the console window should prompt you with the specific forge version required. Just download that version and replace it in the "/mods" folder and restart the server.