The tickets may not yet be ready for dispatch. 

Your seller will be required to deliver these tickets ASAP once they've received them.

The ticket listing will state what type of ticket the seller is selling,  under DELIVERY OPTION 

Tickets sent via Post - The seller must post the tickets as soon as they receive them. The timing for receiving tickets may vary.  

NOTE - If your seller haven't posted the tickets within two weeks of the event, contact Twickets customer support for further assistance.