Google Maps API key without proper referer restrictions is found in the repo. It can be embeded to anyone's website and if the billing account is active, it will incur charges on your account.
Visit this link to verify that you can use the service by visiting the following link: Vulnerable API POC Link
However with the proper restrictions, it should return a Forbidden error.
Attacker is able to consume your daily free quota of 100, charge your account and then abuse your key for their usage.