JAL transit Haneda - Narita

I have book the JAL round trip flight ticket Takamatsu - Tokyo - Hanoi.
And the ticket issue mention that: "The passenger have to pay for transit between Haneda and Narita."
Please teach me about this matter.

Hi!

I hope you have a long enough layover between your flights.

http://www.haneda-airport.jp/inter/en/access/traffic.html

Good luck!

And the ticket issue mention that: "The passenger have to pay for transit between Haneda and Narita."
Please teach me about this matter.

There are two airports in Tokyo area, Haneda and Narita. These two are about 80 km apart. So if your flight from Hanoi lands at Narita and your flight to Takamatsu departs Haneda, you must move from Narita to Haneda. There are many ways to do, the easiest would be the limousine bus while the cheapest would be Keisei/subway/Keikyu trains. In any case the flight ticket does not cover the transportation from Narita to Haneda you have to pay for transit between Haneda and Narita. It would be about 3000 yen and 1 hour for the limousine bus and 1500 yen and 1.5-2 hours for the trains.