ORA-00936 when trying to use EVALUATE

Question

I need an evaluation of purchase contracts (Einkaufsverträge) and the corresponding sales contracts, where the Einkaufsverträge will be extended.

Therefore, I want to create a query that returns a row from the nag_einkaufsverträge table if the expression in the vertragsverlaengerung column (vertrag extension column) evaluates to true for the data item.

I used this query:

SELECT * 
FROM nag_einkaufsvertraege
WHERE EVALUATE (nag_einkaufsvertraege.vertragsverlaengerung, <data item>) = 1;

but then it shows error ORA-00936 – missing expression.

My table looks more or less like this:

I'm using SQL Tools 1.8 b38

Could someone please help to write the right query? I'm lost. Thank you.