Format your Micro SD with its allocation unit size to 64 bytes and its file system to FAT. Convert your roms again. If it doesn't work, try putting a folded little paper inside your cartridge to make it push the pcb to make the gba recognize the pads correctly.
Try this: Backup your micro SD, format it with its allocation unit size to 64 bytes and its file system to FAT (not FAT32 or exFAT) and pass your files to your micro SD. Please give me feedback if this works.
