Plugin marked as v1.20.6 compatible, but it fails to load due to API version 1.21?

[DaanKrivaan]

Hi!

I'm trying to use OldGenerator on Paper v1.20.6 server, but the plugin won’t load because it declares api-version: 1.21, which Paper 1.20.6 does not support. At lest it's what I understand from the log attached below - sorry if I've mixed anything up, I'm not a pro.

Server: Paper v1.20.6
Java version: openjdk version "23.0.2" 2025-01-21
Spigot page lists: Native Major MC Version: 1.21 + Tested Major Versions: 1.20, 1.20.6, 1.21
Multiverse-Core: v5.3.4

I have The End disabled in "server.properties" and "Nether" disabled in "bukkit.yml" - if it matters at all.

However, trying to load it gives this error:
[06:16:56 ERROR]: [ModernPluginLoadingStrategy] Could not load plugin 'oldgenerator-1.2.0.jar' in folder 'plugins.paper-remapped' org.bukkit.plugin.InvalidPluginException: Unsupported API version 1.21 at org.bukkit.craftbukkit.util.CraftMagicNumbers.checkSupported(CraftMagicNumbers.java:389) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c] at io.papermc.paper.plugin.provider.type.spigot.SpigotPluginProvider.createInstance(SpigotPluginProvider.java:121) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c] at io.papermc.paper.plugin.provider.type.spigot.SpigotPluginProvider.createInstance(SpigotPluginProvider.java:35) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c] at io.papermc.paper.plugin.entrypoint.strategy.modern.ModernPluginLoadingStrategy.loadProviders(ModernPluginLoadingStrategy.java:116) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c] at io.papermc.paper.plugin.storage.SimpleProviderStorage.enter(SimpleProviderStorage.java:38) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c] at io.papermc.paper.plugin.entrypoint.LaunchEntryPointHandler.enter(LaunchEntryPointHandler.java:36) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c] at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:532) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c] at net.minecraft.server.dedicated.DedicatedServer.initServer(DedicatedServer.java:286) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c] at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1136) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c] at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:323) ~[paper-1.20.6.jar:1.20.6-151-a4f0f5c] at java.base/java.lang.Thread.run(Thread.java:1575) ~[?:?]

Could you clarify whether v1.20.6 is still supported, or if the plugin now requires 1.21+?

Thanks!

P.S. If you want, I can also add more info / check some settings, etc.