URL query does not filter as expected

I have made a small api together with a collection in mongodb which I named just ‘test’. Every document in it has two fields – ‘letter’ and ‘nmbr’, the value of ‘letter’ being either ‘x’ or ‘z’ or ‘y’, and the value of ‘nmbr’ either a positive integer or a negative integer. Then I wrote this piece of code:

app.get('/tests/:par?nmbr[gt]=0', (req, res) => { Test.find({letter: req.params.par, nmbr: {$gt: 0}}) .then(data => res.status(200).json({data})); });

When I sent this GET request in postman – localhost:5000/tests/x?nmbr[gt]=0, I expected to receive as a response only those documents, in which the value of ‘letter’ is ‘x’ and the value of ‘nmbr’ is a positive integer.
Instead, in the response were included not only those documents, in which the value of ‘letter’ is ‘x’, but also the documents in which the value of ‘nmbr’ is a negative number.
So my question is why? Where did I go wrong?