Unfortunately, there is this GATT error. It is a Bluetooth problem (but, unfortunately, we cannot control it).
We recommend that you begin with restarting the Bluetooth (off and on again), connect to your Monimoto in the app (app> settings> connect) and try to update the firmware again.
If this does not help, try this:
Configuring the device in DFU mode:

Remove one of the batteries >
Wait 30 seconds >
Press and HOLD the button next to the SIM card (do not release it until you are notified to do so) >
Put the battery in >
Wait 2 seconds >
Release the button.

The red and green lights should blink together.

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Now go to the Monimoto app home screen >
'Hamburger' menu in the upper left corner >
Right upper corner 'head' menu >
Restore firmware button >
There should be all possible Monimoto devices in DFU mode >
Choose the device to update