I am running 1.12.2 and my server is the same version.

Whenever I log onto the server and I move, it spams the console with this:
[17:48:25 ERROR]: Could not pass event PlayerMoveEvent to VoidSpawn v1.18.3
java.lang.NoClassDefFoundError: org/bukkit/Tag
at com.endercrest.voidspawn.MoveListener.isConflictingBlock(MoveListener.java:25) ~[?:?]
at com.endercrest.voidspawn.MoveListener.onMoveEvent(MoveListener.java:19) ~[?:?]
at com.destroystokyo.paper.event.executor.asm.generated.GeneratedEventExecutor102.execute(Unknown Source) ~[?:?]
at org.bukkit.plugin.EventExecutor$2.execute(EventExecutor.java:70) ~[patched_1.12.2.jar:git-Paper-1618]
at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:78) ~[patched_1.12.2.jar:git-Paper-1618]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[patched_1.12.2.jar:git-Paper-1618]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:513) ~[patched_1.12.2.jar:git-Paper-1618]
at net.minecraft.server.v1_12_R1.PlayerConnection.a(PlayerConnection.java:711) ~[patched_1.12.2.jar:git-Paper-1618]
at net.minecraft.server.v1_12_R1.PacketPlayInFlying.a(SourceFile:126) ~[patched_1.12.2.jar:git-Paper-1618]
at net.minecraft.server.v1_12_R1.PacketPlayInFlying$PacketPlayInLook.a(SourceFile:88) ~[patched_1.12.2.jar:git-Paper-1618]
at net.minecraft.server.v1_12_R1.PlayerConnectionUtils.lambda$ensureMainThread$0(PlayerConnectionUtils.java:14) ~[patched_1.12.2.jar:git-Paper-1618]
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) ~[?:1.8.0_241]
at java.util.concurrent.FutureTask.run(Unknown Source) ~[?:1.8.0_241]
at net.minecraft.server.v1_12_R1.SystemUtils.a(SourceFile:46) ~[patched_1.12.2.jar:git-Paper-1618]
at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:850) ~[patched_1.12.2.jar:git-Paper-1618]
at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:423) ~[patched_1.12.2.jar:git-Paper-1618]
at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:774) ~[patched_1.12.2.jar:git-Paper-1618]
at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:666) ~[patched_1.12.2.jar:git-Paper-1618]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_241]

And when I configure it to teleport me to spawn using the vs mode command and I jump in the void, it tells me this: [VoidSpawn] Error while teleporting player: Mode has not been setup completely
[VoidSpawn] Details, World: spawn, Mode: Spawn and sends a similar message in chat.

Hey, the latest versions of VoidSpawn only supports MC 1.13 and above. VoidSpawn v1.16.1 is the last supported version for MC 1.12 or below. You can download that at https://www.spigotmc.org/resources/voidspawn.19350/history.