I have a formula that shows as:
{=A5-INDEX(A5:A400,MATCH(TRUE,K5:K4000,0))}

It works but I want to change it to:
{=A5-INDEX(A5:A400,MATCH(TRUE,J5:J400B6,0))}

Problem is that when I click to edit the formula, the {} brackets disappear
and then the formula returns $VALUE!.

Why do these brackets show up and how do I edit this formula?

Thanks, any help would be appreciated!