Joying testing 4G-LTE 3G for android car stereo head unit with sim card

You must turn off the car( off power on to head unit), then insert in the 4G Sim card in slot of head unit, then open the car stereo, it will get the 4G or 3G signal.
https://www.joyingauto.com/
https://www.joyingauto.eu/

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4g lte