I know absolutely nothing about MongoDB, but I can tell you that you're trying to call a method on something that doesn't have any (a plain hash reference).

In the MongoDB documentation's SYNOPSYS, it shows that to delete a document, you call the method against the collection ($coll) object like this: $coll->delete_one({ name => 'value' });

For completeness, here's the expanded documentation specifically for the delete_one() method.

When in doubt, RTFM ;)