XM has set the initial balance to be minus 10 units.
This is for covering withdrawal fees which you need to cover.
By deducting 10 units, XM is avoiding XM Cards to have actual negative balance.
If you transfer 100USD into the XM card, 10USD will be deducted and 90USD will be the available balance.
10USD will be reserved to cover withdrawal fees.
For more information, please visit XM’s official website.