I am currently working on a pixelmon server and I came upon this issue , I have no clue what is going on and I know that I have forge installed , spongeapi 5.0.0 installed and spongeforge installed. But it’s almost like it’s not detecting it or something. (This probably has an incredibly easy fix i’m just to blind to see it.)
Your SpongeForge looks pretty old try updating it
Keeping spongeforge up to date is really important.
Nucleus is simply not compatible with the Sponge you are using. It requires API 5.1, and you are using a very, very old version of API 5.0 - that was dropped two months ago.