I only have this mod and the fabric-api activated, and it seems to crash the server, will it works without issue on the client.
My server run on a basic fabric 1.19.4 version on lilypad host.
The mod version is fabric 1.19.4-1.4.2.
I have no clue where does the issue comes from...

Here's the crash log:

[Pterodactyl Daemon]: Checking server disk space usage, this could take a few seconds...
[Pterodactyl Daemon]: Updating process configuration files...
[Pterodactyl Daemon]: Ensuring file permissions are set correctly, this could take a few seconds...
container@lilypad~ Server marked as starting...
[Pterodactyl Daemon]: Pulling Docker container image, this could take a few minutes to complete...
[Pterodactyl Daemon]: Finished pulling Docker container image
container@pterodactyl~ java -version
openjdk version "17.0.11" 2024-04-16
OpenJDK Runtime Environment Temurin-17.0.11+9 (build 17.0.11+9)
OpenJDK 64-Bit Server VM Temurin-17.0.11+9 (build 17.0.11+9, mixed mode, sharing)
container@pterodactyl~ java -Xms128M -Xmx8192M -Dterminal.jline=false -Dterminal.ansi=true -jar fabric-server-launch.jar
Starting net.fabricmc.loader.impl.game.minecraft.BundlerClassPathCapture
[22:25:06] [main/INFO]: Loading Minecraft 1.19.4 with Fabric Loader 0.16.5
[22:25:06] [main/INFO]: Loading 43 mods:
- fabric-api 0.87.2+1.19.4
|-- fabric-api-base 0.4.28+737a6ee8f4
|-- fabric-api-lookup-api-v1 1.6.29+504944c8f4
|-- fabric-biome-api-v1 13.0.10+6b242079f4
|-- fabric-block-api-v1 1.0.8+e022e5d1f4
|-- fabric-blockrenderlayer-v1 1.1.38+10ce000ff4
|-- fabric-client-tags-api-v1 1.1.1+0eee1254f4
|-- fabric-command-api-v1 1.2.31+f71b366ff4
|-- fabric-command-api-v2 2.2.10+10ce000ff4
|-- fabric-commands-v0 0.2.48+df3654b3f4
|-- fabric-containers-v0 0.1.59+df3654b3f4
|-- fabric-content-registries-v0 3.5.14+10ce000ff4
|-- fabric-convention-tags-v1 1.5.3+6d727b51f4
|-- fabric-crash-report-info-v1 0.2.17+aeb40ebef4
|-- fabric-data-generation-api-v1 11.5.2+26f09d40f4
|-- fabric-dimensions-v1 2.1.50+44c9c860f4
|-- fabric-entity-events-v1 1.5.17+10ce000ff4
|-- fabric-events-interaction-v0 0.6.1+4b6b93f0f4
|-- fabric-events-lifecycle-v0 0.2.56+df3654b3f4
|-- fabric-game-rule-api-v1 1.0.36+3f657af2f4
|-- fabric-item-api-v1 2.1.21+10ce000ff4
|-- fabric-item-group-api-v1 3.0.10+8400c67ef4
|-- fabric-key-binding-api-v1 1.0.35+504944c8f4
|-- fabric-keybindings-v0 0.2.33+df3654b3f4
|-- fabric-lifecycle-events-v1 2.2.19+10ce000ff4
|-- fabric-loot-api-v2 1.1.32+10ce000ff4
|-- fabric-loot-tables-v1 1.1.36+9e7660c6f4
|-- fabric-message-api-v1 5.1.5+53c11dadf4
|-- fabric-mining-level-api-v1 2.1.44+10ce000ff4
|-- fabric-model-loading-api-v1 1.0.2+3a1ea2f1f4
|-- fabric-models-v0 0.4.1+a0255436f4
|-- fabric-networking-api-v1 1.3.6+ae9c4c6af4
|-- fabric-networking-v0 0.3.46+df3654b3f4
|-- fabric-object-builder-api-v1 7.1.1+d63b52eaf4
|-- fabric-particles-v1 1.1.1+86d48884f4
|-- fabric-recipe-api-v1 1.0.13+10ce000ff4
|-- fabric-registry-sync-v0 2.3.2+95ae8716f4
|-- fabric-renderer-api-v1 2.4.2+90110d8df4
|-- fabric-renderer-indigo 1.4.2+90110d8df4
|-- fabric-renderer-registries-v1 3.2.42+df3654b3f4
|-- fabric-rendering-data-attachment-v1 0.3.32+10ce000ff4
|-- fabric-rendering-fluids-v1 3.0.25+10ce000ff4
|-- fabric-rendering-v0 1.1.45+df3654b3f4
|-- fabric-rendering-v1 2.1.5+10ce000ff4
|-- fabric-resource-conditions-api-v1 2.3.3+10ce000ff4
|-- fabric-resource-loader-v0 0.11.7+8400c67ef4
|-- fabric-screen-api-v1 1.0.49+10ce000ff4
|-- fabric-screen-handler-api-v1 1.3.25+10ce000ff4
|-- fabric-sound-api-v1 1.0.11+10ce000ff4
|-- fabric-transfer-api-v1 3.3.1+602c17c7f4
-- fabric-transitive-access-wideners-v1 3.3.0+1b5f819af4
- fabricloader 0.16.5
-- mixinextras 0.4.1
- java 17
- minecraft 1.19.4
- usefulslime 1.4.2
[22:25:06] [main/INFO]: SpongePowered MIXIN Subsystem Version=0.8.7 Source=file:/home/container/libraries/net/fabricmc/sponge-mixin/0.15.3+mixin.0.8.7/sponge-mixin-0.15.3+mixin.0.8.7.jar Service=Knot/Fabric Env=SERVER
[22:25:06] [main/INFO]: Compatibility level set to JAVA_16
[22:25:06] [main/INFO]: Compatibility level set to JAVA_17
[22:25:06] [main/INFO]: Initializing MixinExtras via com.llamalad7.mixinextras.service.MixinExtrasServiceImpl(version=0.4.1).
[22:25:07] [main/WARN]: Error loading class: net/minecraft/class_310 (java.lang.ClassNotFoundException: net/minecraft/class_310)
[22:25:07] [main/ERROR]: Failed to start the minecraft server
java.lang.RuntimeException: Mixin transformation of net.minecraft.class_1657 failed
at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:427) ~[fabric-loader-0.16.5.jar:?]
at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.tryLoadClass(KnotClassDelegate.java:323) ~[fabric-loader-0.16.5.jar:?]
at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.loadClass(KnotClassDelegate.java:218) ~[fabric-loader-0.16.5.jar:?]
at net.fabricmc.loader.impl.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:119) ~[fabric-loader-0.16.5.jar:?]
at java.lang.ClassLoader.loadClass(ClassLoader.java:525) ~[?:?]
at net.minecraft.class_2966.method_12851(class_2966.java:46) ~[server-intermediary.jar:?]
at net.minecraft.server.Main.main(Main.java:109) ~[server-intermediary.jar:?]
at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:480) ~[fabric-loader-0.16.5.jar:?]
at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:74) ~[fabric-loader-0.16.5.jar:?]
at net.fabricmc.loader.impl.launch.knot.KnotServer.main(KnotServer.java:23) ~[fabric-loader-0.16.5.jar:?]
at net.fabricmc.loader.impl.launch.server.FabricServerLauncher.main(FabricServerLauncher.java:69) ~[fabric-loader-0.16.5.jar:?]
at net.fabricmc.installer.ServerLauncher.main(ServerLauncher.java:69) ~[fabric-server-launch.jar:1.0.1]
Caused by: org.spongepowered.asm.mixin.transformer.throwables.MixinTransformerError: An unexpected critical error was encountered
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:392) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:234) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:202) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:422) ~[fabric-loader-0.16.5.jar:?]
... 11 more
Caused by: org.spongepowered.asm.mixin.transformer.throwables.MixinPreProcessorException: Attach error for usefulslimeCommon.mixins.json:ClimbingPlayerMixin from mod usefulslime during activity: [Transform -> Method method_6101()Z -> INVOKESTATIC -> net/minecraft/class_310::method_1551:()Lnet/minecraft/class_310;]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attach(MixinPreProcessorStandard.java:313) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.createContextFor(MixinPreProcessorStandard.java:277) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinInfo.createContextFor(MixinInfo.java:1292) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.apply(MixinApplicatorStandard.java:203) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.TargetClassContext.apply(TargetClassContext.java:437) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.TargetClassContext.applyMixins(TargetClassContext.java:418) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:363) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:234) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:202) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:422) ~[fabric-loader-0.16.5.jar:?]
... 11 more
Caused by: java.lang.RuntimeException: java.lang.ClassNotFoundException: net.minecraft.class_310
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.transformMemberReference(MixinPreProcessorStandard.java:791) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.transformMethod(MixinPreProcessorStandard.java:777) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.transform(MixinPreProcessorStandard.java:743) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attach(MixinPreProcessorStandard.java:307) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.createContextFor(MixinPreProcessorStandard.java:277) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinInfo.createContextFor(MixinInfo.java:1292) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.apply(MixinApplicatorStandard.java:203) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.TargetClassContext.apply(TargetClassContext.java:437) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.TargetClassContext.applyMixins(TargetClassContext.java:418) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:363) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:234) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:202) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:422) ~[fabric-loader-0.16.5.jar:?]
... 11 more
Caused by: java.lang.ClassNotFoundException: net.minecraft.class_310
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.transformMemberReference(MixinPreProcessorStandard.java:791) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.transformMethod(MixinPreProcessorStandard.java:777) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.transform(MixinPreProcessorStandard.java:743) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attach(MixinPreProcessorStandard.java:307) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.createContextFor(MixinPreProcessorStandard.java:277) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinInfo.createContextFor(MixinInfo.java:1292) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.apply(MixinApplicatorStandard.java:203) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.TargetClassContext.apply(TargetClassContext.java:437) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.TargetClassContext.applyMixins(TargetClassContext.java:418) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinProcessor.applyMixins(MixinProcessor.java:363) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClass(MixinTransformer.java:234) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:202) ~[sponge-mixin-0.15.3+mixin.0.8.7.jar:0.15.3+mixin.0.8.7]
at net.fabricmc.loader.impl.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:422) [fabric-loader-0.16.5.jar:?]
... 11 more
container@lilypad Server marked as offline...
[Pterodactyl Daemon]: ---------- Detected server process in a crashed state! ----------
[Pterodactyl Daemon]: Exit code: 0
[Pterodactyl Daemon]: Out of memory: false
[Pterodactyl Daemon]: Aborting automatic restart, last crash occurred less than 60 seconds ago.

yeah... those versions of the mod were poorly written and are unstable in multiplayer. Unfortunately, I don't have time right now to fix it. Thanks for reporting this and providing the crash report though.