You can use the Android NXP Tag info App on a your phone to check if a MIFARE Card has its default keys if you are having issues encoding Smart cards. If the keys are not the default FF FF FF FF FF FF Value you may not be able to encode them.
The app can be found here or in Google Pay Store.
Install and open the app and click the 'Full Scan' tab first and tap a blank card on the back of your phone. The phone should ping and report back info about the card.
A blank card will have Factory Default Keys of FF FF FF FF FF FF on all sectors 0-15. You can scroll down to view all 16 sectors and verify each sector has factory default keys.
If you remove the cards from the hopper and scan them all you need to check if they all have the default keys set. Any that do not will fail to encode.
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