Welcome to the forum.
Try creating a folder called Map on your FAT 32 formatted SD card and put the Supplemental Map gmapsupp.img there.
File location from garmindevice.xml
Your device is capable of using NT & NTU(Unicode)maps for Europe.That is what I would use,
Did you set your PC to not to hide file extensions as it is easy to rename it gmapsupp.img.img by mistake
Files required for your device on SD card