The API does require an address currently. I believe this is because it returns data based on polling locations (precinct). However, if you were to provide the state legislative office address for each state, for example, as an address, you would get the Senators and Members of Congress for all 50 states. That said, you could likely more easily get contact data from their congressional websites.
Be aware, most congressional offices uses inbox management software that screens for spam, security threats, etc. Many public offices no longer make email addresses public. And, even if you do find out the address, the email would not be received unless you are a verified sender. Instead they offer a web form on their official website. So, if you cannot find an email or other readily available contact method, it is likely that the web form is the main contact method.