HI. I contacted placeholderapi and they told me to contact staff + I don't know what to do!. this error:

[PlaceholderAPI] Failed to load expansion class StaffPlusPlusPapi (Is a dependency missing?)
[01:23:32 ERROR]: [PlaceholderAPI]
java.lang.NoClassDefFoundError: net/shortninja/staffplusplus/IStaffPlus
at net.shortninja.staffplus.papi.StaffPlusPlusPapi.canRegister(StaffPlusPlusPapi.java:35) ~[?:?]
at me.clip.placeholderapi.expansion.manager.LocalExpansionManager.register(LocalExpansionManager.java:194) ~[?:?]
at me.clip.placeholderapi.expansion.PlaceholderExpansion.register(PlaceholderExpansion.java:138) ~[?:?]
at me.clip.placeholderapi.expansion.manager.LocalExpansionManager.register(LocalExpansionManager.java:168) ~[?:?]
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[?:1.8.0_292]
at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175) ~[?:1.8.0_292]
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1384) ~[?:1.8.0_292]
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482) ~[?:1.8.0_292]
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472) ~[?:1.8.0_292]
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) ~[?:1.8.0_292]

at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[?:1.8.0_292]
at java.util.stream.LongPipeline.reduce(LongPipeline.java:461) ~[?:1.8.0_292]
at java.util.stream.LongPipeline.sum(LongPipeline.java:419) ~[?:1.8.0_292]
at java.util.stream.ReferencePipeline.count(ReferencePipeline.java:593) ~[?:1.8.0_292]
[21:40]
at me.clip.placeholderapi.expansion.manager.LocalExpansionManager.lambda$registerAll$3(LocalExpansionManager.java:327) ~[?:?]
at me.clip.placeholderapi.util.Futures.lambda$null$0(Futures.java:46) ~[?:?]
at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:59) [patched.jar:git-PaperSpigot-"4c7641d"]
at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:352) [patched.jar:git-PaperSpigot-"4c7641d"]
at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:783) [patched.jar:git-PaperSpigot-"4c7641d"]
at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:378) [patched.jar:git-PaperSpigot-"4c7641d"]
at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:713) [patched.jar:git-PaperSpigot-"4c7641d"]
at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:616) [patched.jar:git-PaperSpigot-"4c7641d"]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_292]
Caused by: java.lang.ClassNotFoundException: net.shortninja.staffplusplus.IStaffPlus
at java.net.URLClassLoader.findClass(URLClassLoader.java:382) ~[?:1.8.0_292]
at java.lang.ClassLoader.loadClass(ClassLoader.java:418) ~[?:1.8.0_292]
at java.lang.ClassLoader.loadClass(ClassLoader.java:351) ~[?:1.8.0_292]
... 23 more