I've got a problem adding enchanted books into the items.csv file and I don't know what I'm doing wrong.
I used b_protectioniv,403,0,{StoredEnchantments:[{id:0,lvl:4}]} in the file which did not work, and the item meta page of essentials did no good to help
I need to know the right syntax asap. Thx

The command you used looks correct, but I'm not sure that it's possible to use on a sign since it is quite long. I recommend trying to ask on the Discord server if anyone's tried anything similar. Most likely, it's just not supported, so you might need to find another way to give the item (perhaps using a paid kit, or along the lines thereof).

What version of Minecraft are you using? items.csv isn't used on 1.13 or above.

With /i 403 0 {StoredEnchantments:[{id:0,lvl:4}]} it works and gives me the right item but I want to make a [Buy] sign which gives this book to the players

1.12.2