When using Google reCAPTCHA in my form, why is the "Error for site owner: Invalid domain for site key" error shown while loading the form?

When using Google reCAPTCHA in my form, why is the "Error for site owner: Invalid domain for site key" error shown while loading the form?

This error occurs when the form domain for the configured reCAPTCHA key pair is not enabled. Refer to the steps to enable it.