A. Ensure that the card reader is properly connected to your device. Check the connection port and try unplugging and re-plugging the reader. If it’s a Bluetooth reader, ensure Bluetooth is enabled on your iPhone and that the reader is charged.
B. If the card reader continues to disconnect, try resetting the Bluetooth connection. Go to Settings > Bluetooth, find the card reader in the list, and tap 'Forget This Device.' Then, re-pair the device.