Okay, so... it says the problem is with an invalid variable.  Yet "expenses" and "amount" appear right to me.  Can you think of anything else I should check?

Is this Cloud or OnPrem?

Have you at anytime, changed the name of the Variable after you had originally created it?

Yes, that is very likely, but it would have been a few years ago.  I haven't changed much on this form for a few years.  It was quickly put together suddenly in March 2020 when everyone was sent home to work remotely and we had to have a way to get invoices approved without handing paper back and forth between people.  It when through a number of revisions over the next six months and hasn't needed much more than a few tweaks since then.  It is entirely possible that error has been there all this time, in fact I think I did notice it awhile back but left it since it was actually doing the job and I couldn't see a solution so moved on and then forgot about it.

If updating the Formula using the Token picker doesn't change anything, then in the past I've typically had to create a New Field to replace the unresolving field (Likely the Amount field). Of course you have to carry that change all the way through your process and then delete the original Amount field variable if that is the culprit.

I've seen this several times in Cloud but never OnPrem, and have reported it to Laserfiche as a known issue.

Okay, thanks Steve.