It was working fine but the steel chests were the only ones set to merge by default so I enabled merging for the iron chests too and got this error message.
Could someone help lol.

Failed to load mods: Error while running setup for entity prototype "WideChests _high-iron-chest-2" (container): next _upgrade target (WideChests _high-steel-chest-2) must have an item that builds it that isn't hidden.

Here are the mods I am using:

base
aai-loaders
bobinserters
flib
Krastorio2Assets
stdlib
PickerDollies
RecipeBook
WideChests
factoryplanner
Squeak Through
Ultracube

thank you so much!

Nevermind i got it to work in my game. Just had to disable steel chest merging for some reason.

Yes, it seems that some other mod is hiding Steel chests from the game, so it is not possible to upgrade to them.

I'm having the same problem how do you remedy that

If you can figure out which mod is causing this then I'll try to do something about it