Confused about flying within 5 miles of an airport under part 107

Hi, I recently took and passed my part 107 exam. I took the test so I would be able to fly drones commercially for real estate photos. There is an airport in my city that has class E airspace with a floor of 700' AGL. So under this there should be class G airspace that I should be able to fly in up to 400' AGL under part 107, correct? However when I use the B4UFLY app it says "You are within 5 miles of an airport. By law, you must notify the airport operator and air traffic control tower (if one is present) of your flight" . But this goes against other things I have heard saying "Do not contact the ATC flying commercially under part 107...fill out an online airspace authorization form". But then I'm thinking "why do I need an authorization form if I'm not flying controlled airspace?". But I have also heard that I do not need to contact the airport as long as I remain in class G airspace, which I think makes the most sense, but I really really would appreciate it if someone could help me sort this all out. Thank you via /r/drones https://ift.tt/2ZYmnJp