[1.12.2] Issues syncing tileentity data between client and server

Hi everyone,

i'm new to modding and i've started following a tutorial to learn the basics. I've created a fast furnace and a generator, and i'm now trying to add a door with a password on my own (coded_door folder)
I've created a GUI in which I can click on buttons to enter the code. It is stored as a string in the TileEntity. I've followed the same pattern as the previous machines to sync the data from the client side to the server side, but for some reason, it doesn't work.
I've spent about 15 hours trying to debug the code, but as i've said i'm new to this so i don't really know where to look.
Here is the link of the tutorial i've followed : https://www.youtube.com/watch?v=rVis_D00afc&list=PLmaTwVFUUXiBE7m5d_uLIRyujqsPTYX4C&index=1
And here my code : https://github.com/noclone/testmod

Maybe it's a stupid mistake, maybe not, i've got no clue.
Don't hesitate to tell me if you need more information, it's my first topic ever ^^

Thanks for your help