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[ Resource Questions / Help and Support ]
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1.) The version of the Resource: dev version #172

2.) Server Software: Paper 1.15.2

3.) What is the problem that you are having?

Hoppers are broken. I dont really know why, but I do have an error when placing it.

4.) YAML / Configuration: Default generated configs

5.) Error codes: https://pastebin.com/pgb9GG1f

Credit for finding this bug goes to sian2005#9113 on Discord

Has nothing to do with hoppers. It is actually a bug resulting from adding the on-equip, un-equip command identifiers in the previous snapshot.

Resolved in the latest; http://ci.craftationgaming.com/job/ItemJoin/373/

This bug has been officially fixed in the release of ItemJoin v5.0.6.
You can grab it here; https://www.spigotmc.org/resources/itemjoin.12661/download?version=320427

Please read the changelog as the documentation has not been updated yet;
https://github.com/RockinChaos/ItemJoin/wiki/Recent-Changes