Cannot use java library in KFF, java.lang.NoClassDefFoundError

[filloax]

Kotlin for forge version: 5.6.0

Minecraft version: 1.21.1

Hi, I am using a Java library (SocketIO) in my kotlin mod for an additional feature. While adding the library and other required libraries to the gradle implementation works in fabric, doing so in Forge with KFF leads to a `java.lang.NoClassDefFoundError' when trying to use the library's classes.

Relevant file in mod repo

Libraries in question (all requirements of the last 2):

"org.json:json:20231013",
"org.java-websocket:Java-WebSocket:1.5.7",
"com.squareup.okio:okio:3.6.0",
"com.squareup.okhttp3:okhttp:4.12.0",
"io.socket:engine.io-client:2.1.0",
"io.socket:socket.io-client:2.1.1"

Error:

Exception in thread "LiveCheckEgobalego" java.lang.NoClassDefFoundError: io/socket/client/IO$Options
	at TRANSFORMER/[email protected]/com.ruslan.growsseth.http.LiveUpdatesConnection.connect(LiveUpdatesConnection.kt:108)
	at TRANSFORMER/[email protected]/com.ruslan.growsseth.http.LiveUpdatesConnection.start$lambda$18(LiveUpdatesConnection.kt:324)
	at LAYER PLUGIN/kotlin.stdlib/kotlin.concurrent.ThreadsKt$thread$thread$1.run(Thread.kt:30)
  [...]

As I have no real workaround for this other than somehow reimplementing SocketIO in my mod, any idea how to fix it?