Never heard of them.
Not been through BHX since autumn 2019 due to Covid, but can't imagine much has changed. For Avis, Hertz, Europcar etc you go to the appropriate counter close by where you exit from arrivals. Do the paperwork and walk about 5 minutes from the terminal to the Hire Car Car Park, which is next to the entrance of Car Park 4. Find the hut for your hire company and get your keys. You can return to the vehicle to the same place.
The issue is with Green Motion, not the airport. Seems Green Motion have their depot serving Birmingham Airport and Birmingham International on the station side. Hence the need to go from the airport to the station and shuttle to the collection point.
https://greenmotion.co.uk/car-hire/united-kingdom/birmingham-international
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