Yes, I've read it now, so try it. Try to name the folder with maps MAP. if you named it with Garmin, it might not read, usually in the internal memory you have to put it in a folder named Map, and in the SD card it can also be Garmin. It has never happened to me that even on the SD card I have to put the name of the Map folder on the card
Some devices will not read more than 16 GB, your device uses 4.8 and 16 GB SD cards.