Result of a level of detail expression must be an aggregate error message?

Hi All,

I'm picking my head over this calculation as I'm still learning creating Tableau calculations:

I created the formula below:

IF [Status]= "Approved" OR [Status]= "In Progress" THEN [Latest Thinking Amount] END

It's working, however, I want it to stay static when the "Status" filter is changed, so I added a LOD expression, but I get an error that the expression must be an aggregate.

{FIXED [Department]: IF [Status]= "Approved" OR [Status]= "In Progress" THEN [Latest Thinking Amount] END}

I tried to add SUM in from of the IF statement, however, I get the wrong amount.

Can anyone help with this issue?

Much appreciated!