Fans are able to pay on the day at Forest Green Rovers on Sunday (2.00pm kick-off).Supporters need to buy a ticket from the Forest Green ticket office, and then scan the ticket as they enter the away end.
Tickets can also be purchased by clicking here, and supporters can opt to have the tickets sent to their mobile phone or print them themselves.
The tie will feature in the BBC's FA Cup Final Score with Jason Mohammed that day. United will receive £12,500.
Ticket prices are as follows:
Over 65: £10