[1.12.2] How to sync NBT Tags between Client and Server?

[Guest]

Hey, I made a shield with an nbt tag (durability) that gives setMaxDamage() the new value which, works totally fine on Singleplayer but not on a Server somehow.
While the Client shows that the durability was updated(with Tooltip mod) it actually doesn't get updated on the server side and the shield breaks in few hits.
How do i sync them?

 

I Tried using readNBTShareTag() & getNBTShareTag() but don´t know how they work...

 

Code:

 

[Hipposgrumm]

This forum no longer supports 1.12.2. Just 1.18.x and 1.19.x.