I created a new page, entered the shortcode provided from the Settings page, and when I published and then updated the page, I get the following errors:
Warning: Cannot modify header information - headers already sent by (output started at /home/name/public_html/website.com/wp-content/plugins/find-your-reps/includes/admin.php:78) in /home/name/public_html/website.com/wp-admin/post.php on line 233
Warning: Cannot modify header information - headers already sent by (output started at /home/name/public_html/website.com/wp-content/plugins/find-your-reps/includes/admin.php:78) in /home/name/public_html/website.com/wp-includes/pluggable.php on line 896
Even with these errors that plugin does work on the frontend.
FYI, the website I tested this on already has the CongressLookup plugin installed so I'm not sure if this error is related to both plugins accessing the Google Maps API and Sunlight Labs APIs.