Most SD card <2GB is tested without problem. We are not able to test every SD card in the market.
If you find your SD card is not able to show file in M180, make sure SD card is properly formatted in FAT file system. FAT16 is prefered. !! NTFS is NOT supported !!.
If you are sure about compatible issue, please report to our support email with below information:
1) SD card brand and model
2) Photo of your SD card
We will make a compatible and incompatible table for other user.