Yeah I am using the dragon block C mod and made a server specifically so that I can use a custom form plugin and it wont work, IDK if I need this for that purpose or if I did something wrong but the tutorial I watched said that was how to make them work together and I was going to try the 1.8 version just incase but it says 404 not found
that’s interesting, there are versions linked in the Maven metadata that have seemingly been removed 
edit: It looks as if someone at Sponge has deleted all the 1.8 versions, I’ve fixed https://spongedl.neptunepowered.org/
Looking at the forge version that comes with that pack, the sponge link provided is compatible. Meaning its probably a mod incompatibly.