Hello! I can't resolve the problem about 5 days or even more. I was re-reading guide by ItemsAdder installing much times. (https://itemsadder.devs.beer/plugin-usage/resourcepack-hosting/resourcepack-on-dropbox), but it doesn't help.
I have Velocity server, which working on Paper, 1.19.3 version.
List of plugins: EssentialsX and EssentialsXSpawn, ItemsAdder (3.3.1 version), LoneLibs, ProtocolLib, Spark, WorldEdit and WorldGuard. That's all basic plugins and I think it's not reason of the problem.