NamelessMC

For some reason it has this error no matter what I do.

[15:43:01 WARN]: com.namelessmc.spigot.lib.nameless_api.ApiError: An API error occured with error code 6
[15:43:01 WARN]:        at com.namelessmc.spigot.lib.nameless_api.RequestHandler.makeConnection(RequestHandler.java:167)
[15:43:01 WARN]:        at com.namelessmc.spigot.lib.nameless_api.RequestHandler.post(RequestHandler.java:52)
[15:43:01 WARN]:        at com.namelessmc.spigot.lib.nameless_api.NamelessAPI.submitServerInfo(NamelessAPI.java:144)
[15:43:01 WARN]:        at com.namelessmc.spigot.ServerDataSender.lambda$run$1(ServerDataSender.java:106)
[15:43:01 WARN]:        at org.bukkit.craftbukkit.v1_7_R4.scheduler.CraftTask.run(CraftTask.java:71)
[15:43:01 WARN]:        at org.bukkit.craftbukkit.v1_7_R4.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
[15:43:01 WARN]:        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
[15:43:01 WARN]:        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
[15:43:01 WARN]:        at java.base/java.lang.Thread.run(Thread.java:834)