Using a hosting service that uses Multicraft to install mods. It doesnt seem like an optimal way to do things but I did not want to port forward. :-(
The server itself will run after installing Fabric (1.14.1 release 10), but when I add the Fabric API 0.3.0 build 157a to the mods folder the server refuses to start.

28.05 02:57:29 [Multicraft] Loaded config for "Vanilla Minecraft (latest)"
28.05 02:57:29 [Multicraft] Updating eula.txt file
28.05 02:57:31 [Server] main/INFO Loading for game Minecraft 1.14.1
28.05 02:57:32 [Server] main/INFO [FabricLoader] Loading 24 mods: [email protected]+f1618918, [email protected]+f1618918, [email protected]+f1618918, [email protected]+f1618918, [email protected]+45e1a1c8, [email protected]+build.154, [email protected]+f1618918, [email protected], [email protected]+f1618918, [email protected]+f1618918, [email protected]+f1618918, [email protected]+f1618918, [email protected], [email protected]+f1618918, [email protected]+f1618918, [email protected]+9232ac87, [email protected]+build.157a, [email protected]+f1618918, [email protected]+f1618918, [email protected]+f1618918, [email protected]+9232ac87, [email protected]+57f0d19c, [email protected]+f1618918, [email protected]
28.05 02:57:32 [Server] main/WARN Mod notenoughwands (1.7.4.beta) does not respect SemVer - comparison support is limited.
28.05 02:57:32 [Server] main/INFO SpongePowered MIXIN Subsystem Version=0.7.11 Source=file:/jar/fabric-server-launch.jar Service=Knot/Fabric Env=SERVER
28.05 02:57:32 [Server] main/INFO Compatibility level set to JAVA_8
28.05 02:57:32 [Server] main/WARN Mixin config fabric-networking-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-networking-blockentity-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-resource-loader-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-mining-levels-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-containers-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-object-builders-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-rendering-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-item-groups-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config notenoughwands.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-events-interaction-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config appleskin.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-content-registries-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-registry-sync-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-keybindings-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-crash-report-info-v1.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-events-lifecycle-v0.mixins.json does not specify "minVersion" property
28.05 02:57:32 [Server] main/WARN Mixin config fabric-commands-v0.mixins.json does not specify "minVersion" property
28.05 02:57:33 [Server] main/FATAL Mixin apply failed fabric-networking-blockentity-v0.mixins.json:MixinBlockEntity -> net.minecraft.class_2586: org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException @shadow method method_11016 in fabric-networking-blockentity-v0.mixins.json:MixinBlockEntity was not located in the target class net.minecraft.class_2586. Using refmap fabric-networking-blockentity-v0-refmap.json
28.05 02:57:33 [Server] INFO org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException: @shadow method method_11016 in fabric-networking-blockentity-v0.mixins.json:MixinBlockEntity was not located in the target class net.minecraft.class_2586. Using refmap fabric-networking-blockentity-v0-refmap.json
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attachSpecialMethod(MixinPreProcessorStandard.java:387) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attachShadowMethod(MixinPreProcessorStandard.java:363) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attachMethods(MixinPreProcessorStandard.java:296) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attach(MixinPreProcessorStandard.java:264) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.createContextFor(MixinPreProcessorStandard.java:244) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.MixinInfo.createContextFor(MixinInfo.java:1145) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.apply(MixinApplicatorStandard.java:268) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.TargetClassContext.applyMixins(TargetClassContext.java:353) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.MixinTransformer.apply(MixinTransformer.java:724) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.MixinTransformer.applyMixins(MixinTransformer.java:703) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:509) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at net.fabricmc.loader.launch.knot.KnotClassDelegate.loadClassData(KnotClassDelegate.java:179) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at net.fabricmc.loader.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:142) ~[fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_201]
28.05 02:57:33 [Server] INFO at net.minecraft.class_2246.(class_2246.java:91) ~[intermediary-server.jar:?]
28.05 02:57:33 [Server] INFO at net.minecraft.class_2378.method_10237(class_2378.java:77) ~[intermediary-server.jar:?]
28.05 02:57:33 [Server] INFO at net.minecraft.class_2378.method_10238(class_2378.java:117) ~[intermediary-server.jar:?]
28.05 02:57:33 [Server] INFO at java.util.LinkedHashMap$LinkedEntrySet.forEach(Unknown Source) [?:1.8.0_201]
28.05 02:57:33 [Server] INFO at net.minecraft.class_2378.(class_2378.java:116) [intermediary-server.jar:?]
28.05 02:57:33 [Server] INFO at net.minecraft.class_2966.method_12851(class_2966.java:38) [intermediary-server.jar:?]
28.05 02:57:33 [Server] INFO at net.minecraft.server.MinecraftServer.main(MinecraftServer.java:903) [intermediary-server.jar:?]
28.05 02:57:33 [Server] INFO at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_201]
28.05 02:57:33 [Server] INFO at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_201]
28.05 02:57:33 [Server] INFO at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.8.0_201]
28.05 02:57:33 [Server] INFO at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.8.0_201]
28.05 02:57:33 [Server] INFO at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:170) [fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at net.fabricmc.loader.launch.knot.Knot.init(Knot.java:129) [fabric-server-launch.jar:?]
28.05 02:57:33 [Server] INFO at net.fabricmc.loader.launch.knot.KnotServer.main(KnotServer.java:26) [fabric-server-launch.jar:?]
28.05 02:57:33 [Multicraft] Server shut down (starting)
28.05 02:57:33 [Multicraft] Not restarting crashed server.
28.05 02:57:33 [Multicraft] Looks like a crash, check the server console. Return value: 1
28.05 02:57:33 [Multicraft] Server stopped

Delete the .fabric folder and try again

I'm having the same issue. I've tried deleting the .fabric folder, however it doesn't seem to change anything. I've tried reinstalling the server and I got it to work, however whenever I add any mod it gives the same error no matter which mod it is. Any idea what's wrong?

Nvm, fixed it. I guess my server.jar was outdated.