The consequence in an indicative conditional is claimed to be false because the antecedent is false
Example
Form
If A, then B; not A, therefore not B
Treatment
One way to demonstrate the invalidity of this argument form is with a counterexample with true premises but an obviously false conclusion. For example:
If Queen Elizabeth is an American citizen, then she is a human being. Queen Elizabeth is not an American citizen. Therefore, Queen Elizabeth is not a human being.