Actually, if you joined during a certain time span, not certain the exact dates you can sell 1 per 24 hours if you joined after the date you can't sell at all until you buy credits or do one of the nice free offters, the most likely reason is to stop multi abuse of credit and card farming as well as mission abuse. and if you joined before that certain date i believe it is the same can't sell till you get credits. hope that helps.
If you joined after said date, then even if you reach level 46 you still can't sell on the market, but if you do one of the free offers on the main page of Urban Rivals then you can sell or if you buy actual credits that works too. hope that helps.
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