Invalid book tag

This is my first time making a datapack and a resource pack, and i've been messing around with an invitation from Library of ruina.
Problem is whenever I give myself the custom-textured book (using this command: /give @p written_book{display:{Name:'{"text":"Simple Book"}'},author:"Test",pages:["Hello world!"]} 1 ) or even just the book without text, I open it to see what I screenshot-ed... I'm not sure what's causing it or how to fix it and i'm legit stumped now.. help welcome ;w; I have a datapack too, but the datapack worked fine,  and i'm not using the functions of the datapack atm, just the book does this..