Harlowe if syntax with link

Hi,

The action I'm trying to crests is a point-of-view character has a choice to pick up an object in one room, and then in another room (a separate passage) if the object is in hand, another link is available. I'm using a string variable to indicate if the object (a tube of toothpaste) is has been picked up.

At the top of the game (first passage) there's a definition:

<!-- Inventory setup below here: -->
set: $inv_tootpaste is "none"

In a later passage:

Maybe I should take the toothpaste? (click-append: " toothpaste?")[ This is great! It's a full tube! You never know when you might need this. (set: $inv_toothpaste to "full")]

And then a further-on passage has this if statement:

(if: $inv_toothpaste is not "none" [[You could throw the toothpaste at her. ->ThrowToothpaste]])

But a trial of this doesn't seem to be working. How can I debug this further? Is there something obvious I am doing wrong?

Thanks -