Forbidden City tickets

Hello,
I have seen that the entrance in the Forbidden City is limited to a certain number of people every day and that they are selling tickets online.
I have some questions:
1) I would like to know if I need to make that purchase on line or I can buy at the entrance when I am there.
2) If I need to buy the tickets on line in advance, could you buy the tickets for me? (website is just in Chinese).
3) I tried to register on the website, translating each step, but one of the fields [phone number] does not accept in any format. Do you know what is the correct way to fill the phone number in the register?
Sincerely,
Jony Luiz Camaroto
Curitiba - Brazil