E320-96 Replacement infrared key does not work. Help please!

I have got only one key from the previous owner that was and still working fine but I have decided to buy a spare key from the dealer((in case of an emergency), and the key works manualy to open doors and to
turn the ignition but the infrared does not work, than they have exchanged to another that still the infrared not working. Do you know how answer what I should do to make it work, please? Your reply will be really appreciate, Thanks,
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