Latest version of mod
Tried cloth API .34 and .37

[06:38:23] [main/FATAL]: Failed to start the minecraft server
java.lang.RuntimeException: Could not execute entrypoint stage 'main' due to errors, provided by 'prefab'!
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:50) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke(EntrypointUtils.java:33) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointServer.start(EntrypointServer.java:33) ~[fabric-server-launch.jar:?]
at net.minecraft.server.Main.main(Main.java:97) [intermediary-server.jar:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
at java.lang.reflect.Method.invoke(Method.java:567) ~[?:?]
at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:234) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.Knot.launch(Knot.java:153) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.KnotServer.main(KnotServer.java:28) [fabric-server-launch.jar:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
at java.lang.reflect.Method.invoke(Method.java:567) ~[?:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.launch(FabricServerLauncher.java:68) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.setup(FabricServerLauncher.java:114) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.main(FabricServerLauncher.java:56) [fabric-server-launch.jar:?]
Suppressed: java.lang.RuntimeException: Failed to find root directory for mod 'bclib'!
at net.fabricmc.loader.ModContainer.obtainRootPath(ModContainer.java:74) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.ModContainer.getRootPath(ModContainer.java:50) ~[fabric-server-launch.jar:?]
at vazkii.patchouli.common.book.BookRegistry.findFiles(BookRegistry.java:146) ~[Patchouli-1.17-54-FABRIC.jar:?]
at vazkii.patchouli.common.book.BookRegistry.lambda$init$2(BookRegistry.java:49) ~[Patchouli-1.17-54-FABRIC.jar:?]
at java.util.ArrayList.forEach(ArrayList.java:1511) ~[?:?]
at java.util.Collections$UnmodifiableCollection.forEach(Collections.java:1087) ~[?:?]
at vazkii.patchouli.common.book.BookRegistry.init(BookRegistry.java:47) ~[Patchouli-1.17-54-FABRIC.jar:?]
at vazkii.patchouli.common.base.CommonProxy.onInitialize(CommonProxy.java:25) ~[Patchouli-1.17-54-FABRIC.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:47) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke(EntrypointUtils.java:33) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointServer.start(EntrypointServer.java:33) ~[fabric-server-launch.jar:?]
at net.minecraft.server.Main.main(Main.java:97) [intermediary-server.jar:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
at java.lang.reflect.Method.invoke(Method.java:567) ~[?:?]
at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:234) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.Knot.launch(Knot.java:153) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.KnotServer.main(KnotServer.java:28) [fabric-server-launch.jar:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
at java.lang.reflect.Method.invoke(Method.java:567) ~[?:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.launch(FabricServerLauncher.java:68) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.setup(FabricServerLauncher.java:114) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.main(FabricServerLauncher.java:56) [fabric-server-launch.jar:?]
Caused by: java.nio.file.NoSuchFileException: /home/container/mods/bclib-0.2.4.jar
at jdk.nio.zipfs.ZipFileSystem.(ZipFileSystem.java:160) ~[jdk.zipfs:?]
at jdk.nio.zipfs.ZipFileSystemProvider.getZipFileSystem(ZipFileSystemProvider.java:125) ~[jdk.zipfs:?]
at jdk.nio.zipfs.ZipFileSystemProvider.newFileSystem(ZipFileSystemProvider.java:106) ~[jdk.zipfs:?]
at java.nio.file.FileSystems.newFileSystem(FileSystems.java:338) ~[?:?]
at java.nio.file.FileSystems.newFileSystem(FileSystems.java:287) ~[?:?]
at net.fabricmc.loader.util.FileSystemUtil.getJarFileSystem(FileSystemUtil.java:79) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.util.FileSystemUtil.getJarFileSystem(FileSystemUtil.java:66) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.ModContainer.obtainRootPath(ModContainer.java:63) ~[fabric-server-launch.jar:?]
... 25 more
Caused by: java.lang.ExceptionInInitializerError
at com.wuest.prefab.Prefab.onInitialize(Prefab.java:52) ~[prefab-fabric-2.1.0.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:47) ~[fabric-server-launch.jar:?]
... 17 more
Caused by: java.lang.NullPointerException: Cannot invoke "net.minecraft.class_1922.method_8320(net.minecraft.class_2338)" because "world" is null
at net.minecraft.class_4970$class_4971.handler$bcg000$onGetHardness(class_4970.java:3117) ~[intermediary-server.jar:?]
at net.minecraft.class_4970$class_4971.method_26214(class_4970.java) ~[intermediary-server.jar:?]
at com.wuest.prefab.blocks.BlockCustomWall.(BlockCustomWall.java:22) ~[prefab-fabric-2.1.0.jar:?]
at com.wuest.prefab.ModRegistry.(ModRegistry.java:70) ~[prefab-fabric-2.1.0.jar:?]
at com.wuest.prefab.Prefab.onInitialize(Prefab.java:52) ~[prefab-fabric-2.1.0.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:47) ~[fabric-server-launch.jar:?]
... 17 more

Works just fine with this mod list.

It also looks like you are missing a mod file called "bclib" as there are error messages about that in your log output above.

I have all those mods in your screenshot, I also have bclib in my client mods and my server mods.

java.lang.RuntimeException: Could not execute entrypoint stage 'main' due to errors, provided by 'prefab'! Prefab is preventing the server to start.

I think the issue is here

Caused by: java.lang.ExceptionInInitializerError
at com.wuest.prefab.Prefab.onInitialize(Prefab.java:52) ~[prefab-fabric-2.1.0.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:47) ~[fabric-server-launch.jar:?]
... 17 more
Caused by: java.lang.NullPointerException: Cannot invoke "net.minecraft.class_1922.method_8320(net.minecraft.class_2338)" because "world" is null
at net.minecraft.class_4970$class_4971.handler$bcg000$onGetHardness(class_4970.java:3117) ~[intermediary-server.jar:?]
at net.minecraft.class_4970$class_4971.method_26214(class_4970.java) ~[intermediary-server.jar:?]
at com.wuest.prefab.blocks.BlockCustomWall.(BlockCustomWall.java:22) ~[prefab-fabric-2.1.0.jar:?]
at com.wuest.prefab.ModRegistry.(ModRegistry.java:70) ~[prefab-fabric-2.1.0.jar:?]
at com.wuest.prefab.Prefab.onInitialize(Prefab.java:52) ~[prefab-fabric-2.1.0.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:47) ~[fabric-server-launch.jar:?]

So I totally blanked on that you were running this as a dedicated server and not just single player!

I won't have much time over the next few days to look at this but should after I get the code updated to use Mojang code mappings.

@red2blue - I have been trying to duplicate this issue when running a dedicated server with some of the mods I saw in the error log but I haven't been able to duplicate it.

Here are the mods that seem to work with the latest available version of prefab:

I cannot really do much at this time unless you can narrow it down to a specific mod that seems to be causing the incompatibility.

I think its this

"because "world" is null"

Its not finding the world, maybe?

I cannot really narrow it down, I have 150+ mods.

When I put it on just the client, I can go in just fine. i can even preview structures (cannott build obviously) but the mod is working for the client side stuff. Its when it goes on the server it fails.