Sounds like something based on NXP Mifare Classic. You first try a dictionary attack against the fob (most readers use whatever default keys the vendor set), if

Sounds like something based on NXP Mifare Classic. You first try a dictionary attack against the fob (most readers use whatever default keys the vendor set), if that fails, you collect nonces by touching the flipper to a reader, calculate keys in the companion app on your phone, then add keys to the flipper's dictionary. The attacks are called darkside and nested.