Where is it coming from? Tracking numbers vary, depending on the country of origin. What the seller really wants is a Delivery Confirmation number to tell her that your item arrived, - not exactly the same as tracking. Anyway, if it is a 'real' tracking number, once it crosses the border it should work here:
In any case whether or not the number is an actual tracking or delivery confirmation number is not as important as the 45 day time limit for opening an item not received dispute. If the item has not yet arrived,open the dispute no later than day 43,no matter what the seller may be telling you. State that the item has not arrived and you wish a full refund. Once the dispute has been opened,the seller has 7 days to respond and you have a total of 20 days from the time the dispute has been opened to escalate to a claim. Make sure to escalate if the seller has not refunded you or the item has not yet arrived.