Looking at it, your code does work, but it is expecting the variable to be myBackpack, but you have named it mybackpack.Since JS is case sensitive, these two are not the same.
Tu codigo esta bien, el problema es que escribiste mybackpack y es myBackpack tranqui me a pasado mas de una vez
“mybackpack” should be named “myBackpack” as shown in the thing,or it’s wrong.